Hayato is Miu's grandfather, and, like any granddaughter, she loves her grandfather very much. Hayato has raised her since she was found in the snow by her mother and has raised her in martial arts since that day. However, due to his influence on her has caused her to have gained very sharp reflexes that she will throw anyone who sneaks up on her. Miu is also annoyed by her grandfathers tenacity to buy expensive scrolls without her knowledge and waste money from time to time. Hayato also possesses a soft spot for Miu, stating that for anyone to ever marry her would have to first defeat him in battle. He even once threatened to kill a man who was holding her hostage despite being a devoted follower of Katsujinken. He loves his granddaughter very much and worries over her well being when she's hurt or in danger, such as when she was going on the ski trip with her school, Hayato was worried about her panicking about how her mother died in the snow. He was also worried about telling her about her past with Saiga, wondering how she would react with how her father abandoned her and her dying mother. When Miu was taken by Jenazad, Hayato only blamed himself for this and became desperate in his search for her, such as traveling all over the globe in his search for her while angrily shouting out for Jenazads name. When Miu was safe he became mad at Kenichi for holding Miu in his arms then became very happy that she was safe with tears of joy that Kenichi had protected her.
He later becomes the great-grandfather to Miu's daughter. Given the fact Kenichi is the father, it is strongly implied that he was able to finally defeat the elder (if not having gained Miu's or Saiga's permission to marry) in combat.
Saiga is Miu's father. However, Miu is constantly trying to figure out more of her history and who her father is since she's known nothing about her parents since she was little and Hayato doesn't want to tell her everything till she's ready. However, Saiga has shown that he does care for his daughter's well-being, such as helping Sakaki and Kenichi (while disguised as John) find her and protected her from Jenazad's men and even thanked Kenichi for protecting her so well. He said he would only intervene if Miu was ever truely in trouble and has always been watching over her. Once Miu discovered that her father was the leader of Yami, Miu showed little surprise, having suspected it for a while and is now under the assumption that he murdered her mother.
Upon finally meeting her father, Miu was overwhelmed and tried to embrace him, but then went into a blind furry of rage after hearing he killed her mother. Just as Saiga is about to kill her, Okamoto showed up revealing the "Saiga" in front of her is really the leader of the Kuremisago clan, Senzui and that Okamoto is the real Saiga Furinji. At this moment Miu finally discovered that her father really didn't murder her mother and always loved her and Miu, leaving her relieved to see that her father was not the man she thought.
After making peace with her father, Miu later had him become a grandfather to her and Kenichi's daughter.
Shizuha is Miu's mother. Shizuha deeply loved her daughter very much and even said how cute she was before she left her to protect her from getting killed by Senzui disguised as Saiga. Miu deeply misses her mother and, due to her death, has caused her to develop trauma's in blizzards.
Miu fairly gets along with Sakaki due to him being the most "normal" master of Ryozanpaku and how he treats Kenichi. However, when he refuses to do something for her, she can act very intimidating and even cause someone as stern as him to cave in to do what she wants. She also grows upset whenever he lashes out at Kenichi from when he was recovering from Kokin and told him to go easy on him. Sakaki also cares a great deal for Miu, going as far as to go to Tidat to save her with Kenichi and was relieved to see her alright and out of Jenazad's control.
Miu gets along well with Akisame due to his calmness and being one of the more mature masters. Though she will be rather scared of the machines he forces Kenichi to go through. Akisame was also willing to help Miu prepare for the play she's been wanting to play for a while. She was even worried when she saw him losing his calm nature from seeing Ogata's treatment towards Ryuto.
Miu, like Shigure, does not get along with Kensei due to his perverted nature and how he's constantly trying to take pictures of her. However, she does have some respect for him and his wisdom of martial arts and will listen to him on occasions. She's also angry at him for influencing Kenichi to become more perverted and how he's taught him some perverted moves. She is also not above lashing out or even physically assaulting him if she wishes and is typically seen with Shigure when they attack him.
Miu thinks of Apachai as a very gentle man, but also gratefully fears his monstrous strength due to him unable to control it and having put Kenichi in a near death state before but was later gratefully relieved he was finally able to hold back in training with Kenichi. She's sometimes annoyed by his childishness and his enormous apatite due to how he doesn't know any better. She deeply cares for Apachai as a part of her family as she was horrified when she saw him heavily injured from Agaard and was relieved to see him alive and well later.
Miu and Shigure, due to them being the only females at Ryozanpaku, have a sisterly bond and enjoys Shigure's company and tries to help her open up more. Shigure even has offered to help her prepare dinner before. They are typically seen at times in the hot springs talking about things she can't talk to others about, showing that Miu has a strong trust in Shigure. Shigure has even encouraged Miu to respond to Kenichi's feelings knowing Miu also has strong feelings for him just as Kenichi does towards her. However, Miu does seem to fear Shigure's training methods since she doesn't seem to know to hold back much and was relieved to see her and Kenichi alive after her trip, which depressed Shigure. They are also a dangerous duo when they fight together when they typically fend off Kensei's perverted antics. However, Miu is worrying about Shigure's feelings about Kenichi.
Miu met Renka when she came from China to bring Kensei back and when she saw her clinging to Kenichi's arm and wanted to bring him back with her, she was upset but greatly relieved when Kenichi didn't want to go with her, which was something Miu wasn't fully able to understand. Miu continuously becomes irritated, angry and even jealous when Renka constantly tries to do things together with Kenichi causing Miu to (unintentionally) treat Kenichi with anger. When Kenichi told Renka how Miu helped change him and though Renka refused to give up, the two officially became rivals over Kenichi's affection. Miu also has a liking to her hair and plays with her in a cat like manner due to her hair and Renka's habit of chasing moving things and the two become good friends regardless.
When Renka transferred to her school just to get closer to Kenichi it caused Miu to become even more jealous and is constantly making sure she doesn't take Kenichi away from her and even will lash out at Renka and tell her to stay away from him, prompting others to state how Kenichi must be lucky to have those two around him. Renka has shown to actually respect Miu and Kenichi's relationship with each other knowing how they feel for each other but won't stop herself to try to win him over. Renka even told Kenichi she knows how strong Miu is and respects her strength and was worried when she was kidnapped and relieved when she was brought home.
Unlike Kenichi's frequent mistreatment towards Niijima, Miu treats him with kindness most the time. However, like every other character in the series, she comments on his alien and manipulative nature like all the others. She constantly is naive thinking he and Kenichi are "best friends" with the two of them call themselves "bad friends". She will also grow very irritated by his bad habit of keeping things from others such as how he made her fight over a disc that held no importance and she was very angry that he did that and she threw little pieces of the disc at his head constantly. Niijima also tried to win her over from Kenichi, but Miu doesn't like him like that and only responds back as a friend.
Kenichi is the first friend Miu had ever made and has a strong bond with. She first accidentally tossed him from behind and apologize to him and at the same time recognized him from a long time ago. 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. Though she's mostly oblivious of his feelings towards him, early on however, she's repeatedly shown to harbor feelings for him and maybe, even deeper feelings than she lets on, such as becoming very flustered when they are called a couple, unable to understand the relief of Kenichi refusing to go to China with Renka and perhaps most famously, becoming rather possessive 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. Miu even shows jealousy whenever he is around other girls and even is upset when she can't spend time with him.
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. When she thought Kenichi was killed by Hongo, she shed tears of sadness and anger and fought angrily to avenge him while unable to control her emotions from believing he died. As stated by Jenazad'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 Jenazad'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 Jenazad'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.
After the Tidat incident, Miu 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 third fight with Rimi, as Miu was losing being unable to control her Dou ki, Kenichi managed to snap her out of it shouting for her not to be afraid of her ki or Junazard's curse, stating he will be by her side. His words reaching her, Miu stood, in control now and smiled down on Kenichi, stating she heard his voice and managed to defeat Rimi with her new control. Rimi stated that Miu was able to control her ki was because of her love for Kenichi.
In the Epilogue, Miu finally achieves her dream of becoming a beautiful bride and marries Kenichi. The two are now happily married and have a daughter with her husband who is now a master class fighter and successful novelist.
Takeda and Miu were originally enemies, but once Kenichi defeated him and he left Ragnarok, the two eventually became friends and typically is kind and polite towards him and encourages him when he wants to get stronger. However, Miu is oblivious of Takeda's feelings for her despite him outwardly showing it by constantly calling her "honey". He, like Kenichi, constantly tries to look cool in front of her and wanting to protect her and even tries to be gentlemanly towards her only for her to respond back as a friend. However, he restrains himself to let her choose who she wants to be with due to his great respect towards Kenichi. Also, he told Kenichi that if he lost his sparring match, he would tell his true feelings to Miu and, though he lost and said he only said that to motivate him, the look he gave her afterwards proves otherwise.
Kisara and Miu were originally enemies due to Kisara being in Ragnarok and Miu having easily defeated her. Kisara wanted revenge so she decided to ruin Miu's play, but Kenichi stopped her and decided not to. When Miu saw her seeming treating a cat badly, she wanted to kill her, however, once she saw that she was really treating the cat kindly, she decided to stay with her to find a home for it and, eventually, became good friends due to their love for cats and have since then developed a type of sisterly bond. Miu even is aware of Ukita's feelings for her and even supports her to respond to him knowing she has feelings for him also. Kisara even was very worried when she heard Miu was kidnapped and wished Kenichi good luck in finding her and was later happy to have her home. Kisara also like to tease Miu about her feelings for Kenichi despite her bashfully denying them. Kisara and Miu also talk to each other about relationships with each other and even asked Miu if she had done anything special alone with Kenichi since the masters were gone for the time, which caused Miu to be very flustered.
Miu met Ryuto when they both were six and, thinking he was the one who blew the whistle to help her notice the thugs from behind (though it was really Kenichi) thanked him for helping her, causing Ryuto to develop a crush on her. It was this crush that led him and Kenichi to fight over the yin-yang badge she gave Kenichi and eventually end their friendship.
After meeting ten years later when he was Odin of Ragnarok, Miu was shocked seeing how much he hates Kenichi and demanded to know why the badge was so important and he said it was because he did something unforgivable. She later watched his fight with Kenichi and was worried when he was left defeated and if he may have died from the building but was relieved for Kenichi's sake that he survived.
They would meet again during the DofD Tournament and Ryuto would keep her from chasing after Sho. She would demand to know about him and Ryuto would at least tell her about his bloodline and convince her to go back. When Miu followed them to the aquarium for a meeting, she ruined it as Rimi was also there and they got into a fight. Ryuto did admit it was nice seeing her again and Miu helped push his wheelchair due to the pipes on the ground (unknowingly making Rimi jealous). She then stopped when Ryuto left and instead asked Rimi to push her, to which she did happily.
Miu first met show when she wanted to go see her mothers grave with Kenichi. When she saw a bird stuck in a tree she tried to help save it and so did Sho and at that moment, Sho took one look at her and immediately fell in love with her at first sight claiming she had "wings" like him. When he told her he was Yami, she attacked him but once he said he knew her father, she gave in wanting to know more about her father. As she was going away with him on his bike, Kenichi noted sadness in her eyes and she did admit she didn't want to go with him, but she was desperate to know about her father. Once Kenichi convinced her to not leave with him, Sho let her stay, but not before kissing her on the cheek (an act that made Kenichi very angry and even cried blood from his eyes) which made Miu blush and Sho would say to himself about how he believes she belongs on his side. She would wear his earring due to him taking her hairclip and wanting to take it back.
At the DofD Tournament, when they would meet again, Miu would be happy to have regained her hair-clip back and would immediately attack Sho stating as he's YOMI she would defeat him for Kenichi's sake. Sho, realizing he would need to use force, attacks her and knocks her out to kidnap her under the belief she belongs only on their side in the darkness. When Sho almost killed Freya, Thor and Takeda, Miu entered her berserker Dou mode and Sho was actually very happy that she fell into the darkness. He told Kenichi he couldn't bring her back but was shocked that he did and swore they'd settle things in the tournament and told Kenichi that he can’t protect Miu from all those trails before leaving. Once their fight began and Kenichi was almost killed by Sho, Sho told Miu that only he could protect her and said he loves her. Miu, while moved by his love for her, Miu felt something about Shō that she liked (despite what he said), but rejected him after Kenichi already promised her that. Kenichi got back up after Miu shouted for him. She even ran passed Sho and only was worried over Kenichi and was happy Kenichi defeated Sho. However, Sho protected Miu at the last second from a soldier shooting at her and took the bullets for her. As the soldier was defeated and Sho was dying from blood loss, Miu shed tears over his death and watched as he made Kenichi promised to protect Miu since he can't and Kenichi and Miu mourned his death.
Despite being dead, Sho would help Kenichi rise up and remind him to protect Miu from Junazard's control and ultimately helped Kenichi fight to save her from Pengulu.
Seeing that Chikage is similar in terms of not being true to herself, Miu made it her goal to make sure Kenichi wouldn't have to fight her due to his refusal to hurt woman and how she saw that he just wanted to be friends with her. Miu believed only she could get through to her and fight her and when she said she should be true to herself, Chikage told her she's doing the exact same thing as her. This caused Miu to realize that even though she's opened up much more and gained so many friends thanks to Kenichi, she still was not being true to herself and decided the next day at school to no longer braid her hair or wear glasses to prove Chikage wrong, which surprised her. Since then, due to Miu constantly trying to have Chikage open up, she's gradually become more open and started to act more like a child having fun. Chikage even showed compassion towards Kenichi when she was kidnapped by Junazard and wished him good luck in finding her.
Miu and Rimi first met during the hunt for the disc on Yami and, in Rimi's opinion, "love rivals" for Ryuto, which leaves Miu confused as she doesn't have feelings for Ryuto. In there first fight, Miu was impressed at Rimi's speed outmatching hers, but was able to keep up with her and later overwhelm her once she fought seriously. Miu was also mostly focused on getting Rimi's gold shoes due to her need for Ryozanpaku's financial needs (which Thor notes she's just stealing them). Once Thor broke the disc they tried to get, Rimi left, but promised they'd settle things.
In there meeting at the aquarium, Rimi asked Miu what Ryuto is to her and the two began a second battle, but, due to Miu's training under Junazard, Miu overwhelmed her completely and likely would have left serious injuries had Miu not been so focused on the gold shoes. Once Kenichi and Ryuto found them, they had to stop and Rimi left with her, but would cause Rimi to train under Ogata to defeat her and gain Ryuto's affection. In there third confrontation, Rimi would overwhelm Miu due to her new Dou ki and leave Miu unable to keep up this time. Miu would be left shocked and angry at Rimi for letting herself gain such dangerous power despite knowing what it does to her loved ones and finally decided to go all out to defeat her. However, once Rimi also went all out, Miu was overwhelmed to the point of being unable to defend herself from Rimi's brutal assalts. But once Kenichi helped her by telling her not to be afraid of her ki, stating he'd by by her side, Miu was able to regain herself and overwhelm Rimi. However, due to Rimi's obsession with defeating her caused her to unleash the dangerous Seidou Goui technique via Ogata's permission. As Miu was overwhelmed, she wondered how to defeat her without killing her, showing she still didn't want to harm Rimi.
Due to Junazard interfering with Sakaki's and Hongo's fight would cause Hongo to accidentally knee-jerk Kenichi and almost kill him which caused Miu to become enraged and lose control of her emotions and angrily attack Junazard in blind rage only for her to be easily defeated. He would kidnap her and bring her to his country and brainwash her into a heartless killing machine full of rage who he renamed "Bulu". As Bulu, Miu was very loyal to him and did anything he asked without question, even killing people. However, she wasn't able to kill Kenichi due to her feelings for him and her still maintaining her sanity deep down. Junazard would later try to have her killed when she didn't live up to his expectations. However, Kenichi would be able to bring her out of the darkness and back to her old self. Once Junazard was killed, the elder managed to free Miu of her brainwashing completely and now no longer has to worry about Junazard ever hurting her again.