Kenichi isn't seen interacting very much with his parents throughout the series, though it's proven he loves both of them very much which is typical for a child to show towards his parents. With his mother Saori, Kenichi is close towards as she occasionally has the utmost faith in his skills as a fighter and supports any of his decisions he chooses such as his choice to live at Ryozanpaku.
With his father Mototsugu, Kenichi is occasionally annoyed by his over-protective nature and his goofiness. He worries over Kenichi's condition frequently and even tried to bring him home by force after seeing how hard his training was. Regardless, he too supports his choice to train as a martial artist and was the reason Kenichi entered in the DofD Tournament having encouraged his son to prove his worth and face his fears, something Kenichi was grateful for.
Honoka is Kenichi's little sister. The two have shown to bicker at one another on occasions, which is typical for siblings. Despite this, Kenichi loves his little sister very much and is very protective when it comes to her well-being, such as when he found out she was kidnapped by Loki, Kenichi became enraged and was determined to save her and was willing to get a brutal beating just so she wouldn't get hurt. When she was surrounded by sharks on the beach trip, he jumped in to save her without a second thought and even fought a shark to save her. Honoka also loves her brother very much and tends to worry over his well-being from the intense training he does at Ryozanpaku from time to time. She tends to visit to check up on him, watch his training or play games with Apachai or Shigure. She's also jealous of Miu and how pretty she is, believing her to be the reason Kenichi stays at the dojo. However, Kenichi proved that he stays there to become stronger to protect his loved ones and Honoka supports her brother because of this. She also enjoys shopping with him at times.
Shio is Kenichi's Karate Masters and training him in all Karate Styles. While at first Sakaki does not want to take Kenichi as a disciple, this changes after the later's fight against Tsukuba. After unwittingly scaring Kenichi by asking what his opponent stance was like and overreacting when he was told, Sakaki teaches Kenichi the Yamatzuki. Later, he is seen teaching Kenichi a way to defend and attack at the same time with his wrist, an effective tactic while fighting against many opponents. He has a high amount of faith in him, such as placing bets with Akisame about if he'll win and bets on Kenichi, though he will worry over his condition at times.
During this time, he has taught him many things, from how to defend himself against an opponent wielding a sword (or any bladed weapon) to giving advice on girls. At the same time, he tries to be a tough teacher to him. He has to constantly battle his instincts, which means beat anything that so much looks at his disciple funny, sharing this attitude with Apachai, like when he had to be stopped by Ma Kensei from trying to fight Boris Ivanov after he attacked Kenichi without any warning. However, he's seemingly to be the nicest of the master's. When training Kenichi he praising him more than most of the other masters.
He has always told Kenichi that no matter how dangerous the situation is, he must come with him to observe and learn from his fights. However, he cares for Kenichi's well-being, such as telling him not to follow him to his fight with Hongo due to this being too dangerous for him. However, Sakaki remembers what his old Master said to him "You never listen to what your master says Sakaki" he admires Kenichi's bravery to do dangerous situations, such as following him to watch his fight with Hongo and when Kenichi asked the soldiers in Tidat about Miu's location despite them being cruel to others. Sakaki is pushed to the point of rage when kenichi threatened or injured. Some examples are the mercenaries in Tidat and Hermit attacking Kenichi (and intending to kill him) after Miu's play. He actually poured a beer over the mercenaries head and asked "You actually dared to point your gun at my disciple, you little shit?" Sakaki seems to respect Kenichi's injuries in fair fights, however. He even call's him "my cute little disciple" has returned. He even went all out to commemorate that he and Miu had returned safe.
Akisame is Kenichi's Jujutus Master. Kenichi reminded him of himself at that age. He is noted to be one of the more disciplined of the masters and is usually a reliable voice of reason in the dojo. Kenichi seems to be the least he likes to train with due to how harsh and strict his training methods are. He's often the one master he seems to be afraid of the most. Despite this, Kenichi has never questioned his training methods and holds him in high regard as his master. Even Akisame will, on rare occasions praise him for his tenacities or how brave he becomes in fights or in the missions he's with him on.
Kensei is Kenichi Chinese Kenpo Master training in The Soft Style of Chinese Kenpo. Kensei has a close fatherly relationship with Kenichi, though mistreats him comically like everyone else does. He also knows Kenichi better than the others due to the fact that he is usually the one who ends up convincing him to cooperate with their plans, such as when he convinced Kenichi to move into Ryōzanpaku, and will occasionally swindle him into buying the perverted pictures that he has taked (in the DofD arc, Kenichi states that all he ever receives are pictures of Tochumaru posing). He's not above ridiculing his master on some occasion's such as how perverted he is or how he's "draging Ryozanpaku's name in the mud" during the D of D Tournament. He tends to bicker with Kensei in a comical manner due to his treatment of ditching Kenichi at the hot springs and getting him in trouble to save himself. Despite all of this, Kenichi still admits that he never doubted his training methods or beliefs as a master despite his perversion and sly personality, further demonstrating his bond with Kenichi as master and disciple. Kensei is also one of the few who believe in Kenichi's ability to gain Miu's affection one day stating that those that work hard and don't give up can always win the girl.
Apachia is Kenichi's Muay Thia Master training him in just Muay Thai. Kenichi's view on Apachai was orininally that of being afraid of the giant Muay Thai user. However, he's grown to admire Apachai due to his kind-hearted nature and his more kinder treatment towards Kenichi than most of the other masters. However, he's afraid of sparing with Apachai more than most due to Apachai's brutal strength and how he's never been able to hold back causing Kenichi to almost die from Apachai's punchs or Knees. It was thanks to Kenichi that Apachai was finally able to learn how to hold back his strength, something he's been grateful for ever since. Kenichi has a high respect for Apachai just as he does for the rest of the masters, especially due to his kind treatment towards his sister Honoka. During the fight between Kokin and Agaard, after seeing Agaard seemingly kill Apachai, Kenichi cried greatly over the apparent death of his beloved master, showing a strong devotion towards Apachai. He was later greatly relieved to see Apachai alive and well thanks to Akisame's treatments on him and continues to train with his master. Recently, Kenichi has now become strong enough to train with Apachai without being sent flying away and is able to put up a better defense against him.
The elder is quite fond of Kenichi, calling him "Ken-chan" and is the only one who apologizes to him for the Hell that he and the others put him through (despite, as Kenichi puts it, simultaneously holding the rank of the most brutal training). Even though he apologizes for the Hell he's put through, Hayato also has put him through similar brutal training, such as when he took him on more than one training trip, Kenichi noted how horrifying and tough it was to just survive the training. He states that Kenichi reminds him of when he was his age and respects Kenichi for that. He is willing to train Kenichi when he feels like he's the only one that can reach the young man. He even offered Kenichi a chance to date his granddaughter should he win the D of D tournament (though that was a lie as Hayato just used his feelings of her to motivate him to win and again reminded him he must fight and defeat him to marry Miu). However, he is not above scolding Kenichi should he do something reckless, such as fighting a master class fighter and put him under house arrest. However, in truth, Hayato and all the other masters were very proud of Kenichi of fighting a master class opponent and for protecting his friends. However, he tends to not let Kenichi get to close to Miu, his granddaughter, such as reminding him if he wants to be with her, he must defeat him (though this was also due to him having caught Miu kissing him on the cheek, greatly angering Hayato even stop him from hugging Miu), to which Kenichi notes is impossible. He even saved Kenichi's life when he was almost killed after his fight with Ryuto and from Hongo's accidental knee jerk attack. When Kenichi saved Miu from Jenazad's control, Hayato placed his hands on Kenichi's shoulders and tearfully thanked him from the bottom of his heart for protecting his granddaughter.
In the Epiloque, Hayato becomes the great-grandfather to Kenichi's daughter. The fact he married Miu strongly implies Kenichi was finally able to defeat the Elder to gain Miu's hand in marriage.
A bit of a loner, Kenichi trains with Shigure the least. However, she seemingly enjoys training Kenichi whenever he needs her guidence. She was even nice enough to teach Kenichi to swim and when he thanked her, he noticed she smiled for the first time in a while. Shigure's behavior has changed noticeably since Kenichi's arrival, as noted by Miu who once wondered if Shigure sees him as more than her disciple, suggesting she may have developed feelings for the young man. She begins opening up to the others, and even joins them for meals. She become's indignant when the other members of the dojo express relief that Kenichi was alright after a training trip with her, though this could be due to her taking their relief as insult to her mastery. Shigure even allows Kōetsuji to tell Kenichi of her past and is quite candid around him. When Kenichi imitated her during his fight with Odin, she jumped up in joy happy that he was imitating her. She would even bathe right next to him, unconcerned with him seeing her nude and even suggests that they bathe together again. Out of all the masters, Shigure trains Kenichi the least, yet it is implied she yearns to train him, and is disappointed with Kenichi's reluctance (and fear) to use weaponry but often tries to convince him to train more. When she finds the ability to give Kenichi words of advice during her task to revive Kenichi as a martial artist, she pumps her fist triumphantly for succeeding as a teacher to Kenichi. After their trainig trip together, Shigure smiles for the first time noting how the special relationship with Miu is so good between the two.
Kenichi grew to be attracted towards Miu due to how cute she was, but was later because of how brave, strong and kind she was, something he desired to become stronger to protect the weak and people he cares about. She was the first friend he had ever made, and the two eventually developed a strong bond with one another. Miu was even the reason Kenichi decided to move into Ryozanpaku to become stronger. He constantly tries to win her affection by impressing her but she's mostly oblivious of his true feelings for her and just views him as a very good friend, however, she is very kind towards him and often comforts him when he's upset or half-dead from the masters' crazy training methods. She has however over the early part of thier time together, repeatedly hinted towards having feelings for him, maybe deeper than she lets on, such as getting embarrassed and flustered when they are called a couple, not being able to understand the relief she feels when Kenichi refuses to go to China with Renka and perhaps most famously, becoming rather possesive and even jealous of him whenever another girl shows affection for him. She was also very happy and blushed when she heard Kenichi talk about how much he cares for her.
After Kenichi saves her life on the school ski trip, she becomes much more open and physically receptive with him, going as far as to tearfully hug and thank him for saving her and staying alive. Since then, she now acts more happy around him and talks more about personal things that she normally can't tell others. Every time Kenichi is left severly injured, she's always hugging him admitting how glad she is that he's alright. He becomes rather enraged when she's hurt or insulted in any way and is quick to defend her from others that want to harm her. Kenichi's devotion and feelings towards Miu has apparently developed into love due to how much he cares for her.
By the time of Miu being left alone with Kenichi for a while when the masters were missing, in addition to starting to realize Kenichi feelings for her, she appears to have started realizing her own feelings for him, going as far as kissing him on the cheek to show her feelings for him. While they didn't get the discuss the matter further (due to her grandfather witnessing the whole thing and scaring the two), several people at school have since noticed Miu being more cheerful and energetic, as well as as more eager to be around Kenichi. As stated by Junazard's observations of her around him even under his control, Miu's feelings for Kenichi have developed even further and has fallen in love with Kenichi. Even under Junazard's control, Miu was able to hold back due to her feelings for him. Kenichi's devotion towards Miu is so great that he's even willing to die to bring her back to the light and out of Junazard's control. Miu has even stated she does not mind dying for Kenichi so he can live and has the utmost faith in him by placing his hand on her heart to show how much she believes in him.
Since the Tidat incident, Kenichi has become even closer with Miu and she is even more happier around Kenichi and much more closer and even intimate around Kenichi as noted by Ukita. Kenichi himself seems to have finally gained more confidence in himself due to this and even convinced her to ride the merry-go-round together since she's always wanted to, which Miu was very grateful towards and even blushed while riding it with him. During her fight with Rimi, Kenichi managed to save her by telling her not to be afraid of her Dou ki or Junazard's curse, stating he is with her. His words having reached her, Miu stood, having gained control of herself and managed to defeat Rimi.
In the Epiloque, Kenichi was finally able to gain the Elder's permission to marry Miu as the two become happily married in thier young adult years and have a daughter.
She at first treated Kenichi with disdain, but soon warmed up to him due to his bravery and kindness. She even went to his place claiming to bring her father back but quickly showed an affection towards him and trying to win him over with her appeal. Her strong liking to him soon turned into strong love, which she tries to deny. She even helps him with his fighting style and training at times. She is even willing to go fight in his place and bring him back to China. Whenever Kenichi even compliments her and said how grateful he was for her fighting in her place against Rachel, she blushes and wows her even further. He is the only other person other than her father she'll listen to and usually is seen clinging to his arm from time to time, much to Miu's jealousy. Though she has feelings for him, she's aware of his feelings for Miu and respects him enough for that but won't stop trying to win him over for his attention. In an omake, Pisuke (her pet crow he helped save) wished to see him and convey her feelings for him and the message Pisuke gave him from her (while she was asleep at the time) was "I love you, Kenichi", surprising him, as he was left unaware it was Renka's feelings towards him via Pisuke. Though he's unaware of her love for him, Kenichi cares for Renka very much and is very close with her.
Ryuto was the first friend Kenichi ever made which was partly due to the fact Ryuto was shorter and even weaker than him. When they were younger, they saw Miu beat up some thugs and afterwards they desired to become stronger like her. When Kenichi was given the Yin-Yang badge from Miu due to Kenichi giving her the kitty-cat badge Ryuto gave him, Kenichi and Ryuto fought over it and though Kenichi won, he gave the win to Ryuto and Ryuto would grow angry at him and after Kenichi moved away for a while, their friendship grew very sour. Even whe he was Ragnarok's Odin, Kenichi didn't recognize him until they went back to the spot they first met Miu and he desired to fight Kenichi again to reclaim the badge Kenichi got from Miu. After Kenichi lost, Ryuto took the badge and gave Kenichi another Yin-Yang badge that he bent up as a loser's gift. Kenichi then vowed to defeat him again to bring him back to his senses. During their second fight, after hearing that the reason Ryuto wanted the badge and becoming stronger to prove his worth, Kenichi called him an idiot and swore he would defeat him for the sake of their friendship. He gives Kenichi back his Yin Yang badge as a sign of his defeat.
This friendship seems to be revived later on as Ryūto gives back Kenichi's Yin Yang badge after his defeat and during the D of D Tournament, when a wheelchair-bound Ryūto defeats Sho Kano's bodyguards sent to prevent Kenichi from reaching Sho. Kenichi also became enraged after discovering that his body was used as a test subject and expressed his desire to save Ryuto from Yami.
During the visit to the aquarium, Ryuto would call him down to have a talk and as the two were present, they began talking about there past experiences from there childhood and as they seemingly were at peace with each other, they were interupted by the sudden appearance of Miu and Rimi. As they realized they were followed, Ryuto appologized and stated they would have to do this another time.
Their friendship would later fully resurface during the fight in the amusement park, as when Kenichi attempted to fight Ogata, Ryuto saved him and the duo fought together against the Yami master. Though they were defeated, Ryuto was prepared to sacrifice himself to save Kenichi telling him to live just as he was saved by the arrival of Tsutomu Tanaka. Afterwards, the two have been speaking to each other on neutral terms, seemingly reigniting their friendship.
Kenichi viewed Jihan as a dirty fighter and one who was not a worthy martial artist for his dirty fighting styles. Jihan saw Kenichi as a revolutionist who is fighting against his own destiny as a commoner and desired to kill him no matter what. Kenichi also hated his dirty tactics and how he was planning on killing Miu had it not been for Kenichi. Kenichi scoffed at his beliefs and actually pittied him for losing and how he looked down on the prince of Tidat. However, Kenichi did try to save him from dying in Junazard's avalanche, though Jihan refused and threw him on Tanimoto's snowmobile.
In his talk with his sister Radin Tidat Lona he told her that he died as a prince and as a man, showing that despite enemies, he won't speak ill towards him, something Lona thanked him for. He was shocked seeing him alive again after he and the elder arrived to stop the Tidat army and Jihan finally acknowledged Kenichi's skill's as a fighter and showed him respect. However, he still has a habit of calling him a commoner, but did appologize saying he shouldn't be so rude to Kenichi, promting him to note Jihan has "grown up" a little but still the same deep down.
Takeda is one of Kenichi's closest friends and rivals. Though they once were enemies with Takeda a member of Ragnarok, once Kenichi saved his life and helped him get his boxing career back and the usage of his left arm, Takeda has come to deeply respect and admire Kenichi and is always respectful to him. The two always has each others back and enjoy each others company. Kenichi is even the one who inspired Takeda to become stronger to reach Kenichi's level someday and sought out his master James Shiba to become stronger. His respect for Kenichi is to the point of allowing him to do as he wants with his relationship with Miu because of how Kenichi saved his life and his boxing career, however, though Takeda also has feelings for Miu, he stated to Kenichi in their rematch together, should Kenichi lose, he'll tell Miu how he feels about her. This gave Kenichi more of a drive to win in his fight with him and after he won, Takeda said he was lying to just motivate Kenichi, however, the way Takeda looked at Miu later showed otherwise. Nevertheless, Kenichi has shown nothing but the utmost respect for Takeda and knows he can rely on him to protect Miu should something happen to him.
Kenichi has shown to have a rather strong bond with Ukita compared to most in the series. The two are able to talk about things that Kenichi can't talk with about others. Kenichi even tells him things about him that his masters and other members don't know about, showing a strong amount of trust in him. Even Miu doesn't know certain things he's told him that he hasn't told her. The two can also relate about how they feel towards Kisara and Miu respectively. He even gave Kenichi advice on how to deal with Miu and the two can comunicate on a respectful level when they try to impress the girl they like. He also tries to act like Kenichi when the two try to impress the girl they like.
Kenichi was originally enemies with Kisara due to his refusal to hit women and her thinking he was mocking her. This puts her at odds with Kenichi, who refuses to attack women. However, she later develops a degree of respect for Kenichi after their fight, during which he only guards against her attacks in order to stop Kisara from advance to ruin Miu's play. When Miu is kidnapped by Silkwat Junazard, Kisara offers her help to save her. While Kenichi goes with Sakaki to Tidat to save Miu, Kisara and the other alliance members wish him good luck. She doesn't really interact with him much other than when he's with Ukita, the person she has a crush on.
Kenichi's relationship with Niijima is one of the most dynamic relationships of the series. Niijima was one of the worst bullies Kenichi had that picked on him since middle school. Even in high school, Niijima enjoyed messing with Kenichi and calling him "Weak Legs". However, once Kenichi defeated Daimonji, Niijima decided to spread the news to everyone in the school to have all the delinquents come after him and Kenichi would become angry and afraid because of this. Every time Kenichi defeated a powerful opponent in school, Niijima would continuously spread rumors, some true and some false, to make the school fear or respect Kenichi which would cause Kenichi to lash out at Niijima most of the time. Despite this, Kenichi was occasionally willing to listen to Niijima's information he had on the opponents Kenichi would have to fight. When Niijima created the Shinpaku Alliance, Kenichi didn't want to have anything to do with it, and hearing Niijima's plan for world domination, Kenichi would just slap him silly in a comical manner. Kenichi would occasionally just hit Niijima whenever he did something annoying and be one of the comedic reliefs of the series. However, Niijima eventually starts showing more care for Kenichi and developing a respect for him. When Niijima was kidnapped by Ragnarok, Kenichi, though hesitant, told Miu that though Niijima was a "bad friend" he decided to save him because he's his "bad friend".
There relationship gradually grows much better over the coarse of the series to one of good, yet comical and somewhat strained, friendship. In a good portion of Kenichi's fight with YOMI members he shows great concern for his well-being and was horrified when he was presumably killed by Kokin and did everything in his power to bring him back to life (though he also wanted him to stay alive for his ambition) and even prayed that Kenichi would come out alive in his fight with Kōkin. Kenichi also tends to call him, like most characters, evil or an alien due to his alien-like appearance and occasionally gets startled by Niijima's presence from coming in behind him.
Kenichi first met Raichi after the mafia was done chasing him and Renka and he was lost. They quickly bonded due to their love for plants and the two became good friends. However, after seeing that Li Raichi, also known as Spark, was attacking the Shinpaku Alliance, Kenichi, knowing that someone who loves flowers so much, couldn't be a bad person and vowed to fight her despite his refusal to hurt a woman to bring her to her senses. Despite Raichi having the ability to break Kenichi more than once, she was ultimalty unable to kill him, being brought to tears of sadness and frustration over fighting him and, because of his kindness and compassion towards her, admitted defeat as a martial artist. She even refused to help fight him again against her fathers wishes. Kenichi's fight with her had a huge impact on his determination to fight Yami so kind people like her won't be forced down the path of darkness.
They would meet again during Diego's fight with Kensei and she would assist him and Miu in saving the passangers on the ship and fighting Meatman together. She's also told Miu directly that she has feelings for Kenichi now and if Miu won't do anything to win him over, then Raichi will, causing Miu to get jealous.
Kenichi's view on Boris was that of frustration and annoyance by his constance tenacities to follow orders no matter what, even if it meant not fighting Kenichi after he challenged him by giving him his YOMI emblem. Kenichi imediatly became enemies with him for when he attacked Miu at their home and fought to defend her. However, Boris is the only YOMI member to have ever complemented Kenichi's skills as a fighter and siding with Kenichi to protect their teacher Ono-sensei. Though Kenichi was enraged at him trying to kill all his classmates on the school camping trip, he was willing to call off the attack after being defeated by Kenichi, showing that he's earned his respect. Kenichi even noted he left a fairly good influence on the students at his school and actually did several good deeds at his school such as cleaning the windows and the floors, something that left Ono with tears of joy and sadness after he left.
Sho was one of the very few people that Kenichi state he just hated so much for trying to kidnap Miu, hurting his friends, and killing the Pankration team (though it was later revealed that Sho let them leave the island). He first became imediate enemies with him after how he tried to take Miu away from him and kissed her on the cheek before he left, leaving Kenichi enraged and very depressed. That moment left Kenichi being unable to get over due to how much he cares for Miu. Since then, Sho viewed Kenichi as someone unable to protect Miu and constantly attempted to kill him to prove only he can protect Miu. He attempted to bring Miu into the darkness only to be thwarted by Kenichi by bringing her back, showing he knows her more than Sho ever will. Since Kenichi knows Miu more than him he says that he will kill him with one strike which he didn't so he decided to finish him off at the tournament and their rivalry started for Miu and for the title of strongest. Out of all the fighters Kenichi's faced, Sho is by far the strongest opponent Kenichi has ever faced, as he was an opponent who had more masters, trained far longer and much more experience as a fighter and pushed Kenichi beyond his limits to the point of how Kenichi developed his Ryusei Seikuken in his fight with Sho. After defeating him, when Miu was about to be shot by a soldier, Sho got up and shielded her and as he died, he placed out his fist and asked Kenichi to protect Miu in his place, despite the fact that they were enemies, which Kenichi promised. He holds this vow to this date and swore he would become much stronger.
Though Kenichi hated Sho, he told Kokin that though he hated him, his heart was not weak and that he live by his convictions and was a strong man. He even told his master Hongo that show was a strong opponent who was an incredible person and man, stating his actions were not a mistake protecting Miu. Sho even appeared in Kenichi's mind during his attempts to save Miu from Junazards control and even gave him the strength to stand up and fight.
Despite her being in YOMI, Kenichi greatly cares for Chikage and has a desire to bring her out of the darkness. Kenichi told Miu that he views her as a little sister due to her age. Though Chikage occasionally doens't think much of Kenichi and sees him as her enemy and called him "band aid" in the beginning, she's gradually shown more of a caring side towards him and beginning to view him as a friend. However, it is clearly evident that she is starting to question the Killing Fist philosophy and becoming more and more intrigued with the Saving Fist philosophy and with Kenichi himself, though she doesn't want to admit any such thing. She tends to hide her budding friendship with Kenichi with seemingly hostile retorts and reactions. When in her "Child Mode" she's more friendly towards Kenichi. By the time Miu was kidnapped by Junazard, she's become much closer to him, actually showing simpathy towards Kenichi's condition and wishing to help him anyway she can by giving him some candy.
Possibly due to Kenichi's influence, Chikage has become hesistant to kill anyone or those associated with the Shinpaku Alliance, resulting in Mikumo attempting to brainwash her into nothing but a killing machine. However, Chikage refused her masters orders on the grounds to protect her honor, mentioning that she learned that from Kenichi and wishes to follow in his beliefs.
Kenichi grew very angry at Kokin having killed him once as a martial artist and believing he stained his masters fighting styles. He was also angry at Kokin having used his mind games on Kenichi in their first match together and causing Kenichi to want a rematch against him someday. During their second match together, Kenichi became very determined to win his fight with him to reclaim his masters' honor. Kokin is also one of the most dangerous opponents Kenichi's faced since Sho Kona as the latter pushed Kenichi to his limits and how he was able to counter all of Kenichi's moves. When Kenichi declared he would end the fight using only Muay Thai in honor of Apachai's presumed death, Kokin, in a rare moment of emotion, laughed histarically stating he couldn't read him at all. After defeating him using the 2 basic moves Apachai taught him, Kokin commended his moves and admitted defeat as a martial artist, having finally gained his respect as a fighter.
Kenichi seemingly got along well with Ethan compared to most of the other YOMI members. Kenichi describes Ethan as the most honest member in YOMI, as he never did anything bad in Kenichi's school, defended his classmates on the camping trip, and tries to think of peaceful solutions to solve problems, such as having Kenichi die as a martial artist once again as the best solution for both of them. He was also quite polite towards Kenichi, going as far as to appologize for all the trouble his sister has been causing him and his friends. He even genually thanked Kenichi for helping him save his sister and didn't want to cause anymore trouble with him or his friends anymore. When Kenichi brought all the friends Ethan made in school despite him stating that was all an act, Ethan, moved by Kenichi's kindness smiles for the first time at Kenichi and proudly shaked his hand and said goodbye to him and went back to India. Kenichi even showed he would miss him and stated he wasn't a really bad person. However, he was frustrated when he asked Kenichi to look after his sister when he left.
Unlike her brother Ethan, Kenichi does not get along with Rachel due to her attention seeking obsession and how she desires to kill him. However, she does find him interesting on more than one occaision. She's also a huge flirt, having Kenichi (unintentionally) grope her breast and teasing Kenichi about it despite it being an obvious accident and even kissed him on the cheek to make Miu very angry and even jealous. She was very happy not to be the new disciple of the Demon God Fist and after hearing that Miu had been kidnapped by Silcardo, she decided to help the Shinpaku Alliance find her. She thought she would repay them after Sakaki rescued her and she could find out where her master is. She later helps Shinpaku Alliance and informs them of the location Mui may be found at and all inform Kenichi of the location.
Since her helping Kenichi, it seems he's started to view her as a friend, something that left her dumbfounded and in disbelief, likely meaning she was rather moved by his kindness and now unsure of her choice in life.
He also has a great interest in the Shinpaku Alliance, specifically in Kenichi as he was able to beat three YOMI members at the time. Kenichi has yet to meet him, however, Kajima expresses his delight knowing Kenichi had no talent just like him and that they both had to work hard to obtain the level of strength they are now and expressed his regret that they are destined to fight.
Once they did finally meet, Kenichi initially believed he was nice since his master (Saiga) told him to release Shigure. However, once he tried to kill him, Kenichi then engaged battle with him while they both expressed their different views on martial arts was right and chose the winner would be right. However, Kenichi is happy to fight him due to them having such similar backgrounds and viewed as people with no talent.
Kenichi's relationship with Tanimoto, also known as the 6th fist of Ragnarok's Hermit, was very antagonistic after discovering that his seemingly kind personality in school was a lie and how he tried to kill him on a moving bus thinking Kenichi's sense of justice was a lie. Though their fight ended in a draw, Kenichi vowed he'd be the one to defeat him. After Honoka was kidnapped by Loki, Kenichi went to rescue her and seeing Tanimoto at the church she was at, Kenichi became enraged and fought him to save his sister. While fighting him, Kenichi noted that when they fight their fists talk more than their mouths and he noticed that Tanimoto was against Honoka being kidnapped and told him that he needs friends. After seeing Tanimoto save his sister from Number 20, Kenichi seemed to view Tanimoto as a better person. This was proven true as Tanimoto told everyone at their school about the rumors around Kenichi were false (though this was also just so he could have Kenichi to himself). Since then, the two have been considered rivals. Tanimoto even lets Kenichi's sister Honoka hang out at his house whenever he wants since she reminds him of his deceased sister. After his fight with Berserker, Tanimoto even smiled at Kenichi and high fived him to win his fight with Odin. Kenichi likes teasing Tanimoto by calling him "Natsu-chan which causes him to respond "Who the hell is Natsu-chan". He also likes telling others that their "best friends" and when everyone leaves, Tanimoto reacts violently by hitting him to a comical manner. When Kenichi learned of him joining YOMI, he was angry at his actions, but after he heard that he hasn't caused any trouble yet, he realized he had a reason for what he was doing and trusted his judgement. Regardless, the two are close with Tanimoto having grown comfortable around him and at times enjoying his company at his home and even smiled after seeing his resolve to save Miu from Junazard.
Though Kenichi seems to think he still cares for Ryozanpaku, he was shocked when he heard him choose to let Kajima kill Miu should she get in the way of the Eternal Sunset. However, after witnessing that the "Saiga" before him is an imposter named Senzui and the real Saiga was non other than Okamoto resulted in Kenichi becoming relieved in the man who he believed was good at heart.
In the Epiloque, Kenichi and Saiga become inlaws with Kenichi marrying Miu and Saiga becoming a grandfather to his daughter.
Having meet Ogata in the woods during his training with the Elder, he was saved by him and viewed him as his lifesaver and held a great respect for him. However, he saw some darkness inside him after he brutally killed a bear and when he asked if Kenichi would like to be his disciple, After he refused and Ogata let him go. After Sho told Kenichi that Ogata is Ryuto's master and how he used him as a test subject leaving him paralized from the waist down, he became enraged and now has a deep grudge against Ogata for what he has did to Ryuto and how Yami ruined his life.
When meeting him for the first time since in the woods, Kenichi boldly approached him and, rather than attempt to fight him, politely thanked him for saving his life in the woods. Ogata then placed his hand on Kenichi's head and admitted his happiness over how well he had grown, to which Kenichi thanks him, but then walks away as the two realize it's due to there differing paths of Katsujinken and Satsujinken.
Once he witnessed Ogata nearly kill Miu, Kenichi flew into rage and fought the S-Class Master. However, he would have been killed had Ryuto and Tanaka had not intervened at that time. Once Kenichi discovered Ogata murdered Tanaka's wife and unborn child, he was furious, but couldn't understand why he couldn't bring himself to fully hate him, questioning if it's cause of his genuine love for martial arts.
Kenichi was shocked and horrified by Jenazad killing Jihan in a avalanche and trying to kill him to. He was also upset when Ethan told him that Jenazad now developed and interest in him. Kenichi then swore for the sake for Miu that he would bring her out of Jenazad's hands even if he died trying. Jenazad has a strong dislike towards him due to him being the reason why he can't control Miu completely due to her feelings for Kenichi and how he reminds him of the Hayato. He even mocks Kenichi's efforts for trying to save Miu, stating he's too weak to do anything for her. However, Kenichi is also the main reason that Miu has finally came back to her oldself. He later became relieved Hongo defeated him and was shocked seeing Jenazad die from his injuries Hongo gave him. With Jenazad dead he can no longer hurt Miu.
Being the master of the late Sho Kano, Hongo at first seemed to have a grudge against Kenichi and Miu for being the reason why Sho died and demanded to know why he died. However, after Kenichi told him that Sho was an incredible man and person and didn't die performing a mistake, he seemed to lessen his view of the boy and see him in another light. Kenichi notes that his aura is terrifyingly intimidating and has an incredibly hard appearance. Kenichi doesn't have any grudge against Hongo for nearly killing him from Junazard's sneek attack, knowing it was accidental. He even wishes for him not to die in his fight with Junazard, calling him "Hongo-san". He was very shock to see Hongo survive his fight with Junazard and the way he used the his leg to kick the last blow to Jenazad.
During the Eternal Sunset, Hongo saved Kenichi from getting killed by Michael Sctilvay and willingly let him fight Kajima and later saved Niijima from getting killed by Saiga.
Despite their initial meeting, Agaard developed a liking towards the boy due to him defeating Bantou's disciple with one move and was injured. He even commented to Apachai that Kenichi is a good disciple and was amazed how Kenichi wanted to fight for revenge for dirtying his masters fighting style by dying once and fights for their honor, stating he's a nice disciple with a sense of duty. Agaard has nothing but the utmost respect for Kenichi as he went as far as to place his hand on his shoulder from behind thanking him from the bottom of his heart stating he's glad that a man like Kenichi is Apachai's disciple. His respect for Kenichi is so great that he was even trying to protect him from the Bantou Master trying to kill him by giving him instructions on defending himself and even silently lamented the thought of being unable to save Apachai's disciple. Though Kenichi was horrified by Agaard's imense Ki and how he occasionally got up close to Kenichi and even almost killed Apachai, Kenichi also seems to hold some respect for Agaard for trying to save him from the Bantou Master.
Despite their initial meeting only once, Sougetsu seems to have a liking to Kenichi. Sougetsu even seems to be rather mused by Kenichi's efforts for trying to save his life in the fire. Knowing he'll die along with him, Sougetsu chose to let him live while showing gratitude on his face for his efforts. Sougetsu is portrayed as somewhat sympathetic, and does somewhat redeem himself by saving Kenichi, the original Sougetsu was given no positive traits whatsoever. He doesn't want Kenichi and Tanimoto to fight in a death match due to his respect towards Kenichi (or his younger brother).