James Shiba (ジェームズ志場, Jēmuzu Shiba) was a former champion boxer famous in the underworld where he got the nickname "The God of Destruction". James' right leg was crippled and right eye lost in a fight with the One Shadow of Yami. Since then he became a hermit, living under a bridge in a shack containing a boxing gym, coming out only to play Pachinko. Takeda's reaction implies that he is one of the few Grand Master-Class Boxers in the world.
Shiba is a tall and lean and muscular man with pale hair parted on the sides and shaved halfway down the middle and a long pointed out mustache which, like Akisame, takes great pride in and is usually pointing upwards. He wears dark pants with knee guards on his knees and dark boots with a ripped sleeveless vest. He has a type of joints inside his right leg and an eye patch over his right eye due to his injuries from Saiga in the past. He's sometimes seen smoking a cigarette.
James is comically shown to be rather dishonorable and arrogant, to the point where Kōetsuji mentions that "even Yami would not accept him for his arrogance" (though his opinion is arguably biased due to a mustache grudge he carries against James). Such is seen in the disciple race between him and Koetsuji, during which he flicks a Pachinko ball at Kenichi's head and causes him to fall over, taking advantage of this to give Takeda the lead. The other example is his refusal to cut off his own mustache despite the bet, by exploiting the wording of the bet and shaving only a few hairs off and then escaped by jumping onto the nearby bullet train. James is also not above taking advantage of Takeda, having him fight in betting matches in order to supplement his own income and becomes quite wealthy because of it.
While as dishonorable as Shiba is, he is capable of being honorable enough to at least save Niijima at the request of Kenichi. He also desires to get revenge extends to resort to any means necessary, having resorted to hold Saiga off as long as he can while Niijima uploads the virus in the weapons system. This shows that despite his own arrogance, he knows his own limitations as he is aware that he cannot defeat Saiga.
James also keeps various pets and names his moves after them, such as the Giant Cat Eye Frog Punch, named after a frog with cat eyes. He apparently hates being called "sensei" as he punches Takeda as soon as he calls him "sensei".
During Takeda's fight with Kenichi, James is shown to care about Takeda by forfeiting the match claiming that it is foolish to break his source of money and forgetting the bet of cutting off his mustache if he lost (comically in a seppuku style), which he blatantly and arrogantly refused after being reminded of it. However, after Takeda's fight with Lugh, Shiba showed the ultimate care towards Takeda by stating how glad he is that he's alright and praised him nonetheless. Even Shiba commented how he's surprised at his caring nature to Takeda. Like Takeda, James's best punch is left straight, the knowledge of which helps form a bond between the disciple and master.
James' mustache and beard also indicate his mood: when they point downward, he is in a neutral or bad mood; when they point upward, he is excited. He also made Takeda wear restraints that exercised his boxing muscles, making his training methods similar to Akisame's due to how hellish it is. James harbors a deep grudge against Saiga, as he is willing to do anything to get back at him. James is willing to leave the battle against the Nine Fist and the Hachiou Executioner Blade to fight Saiga Furinji leaving them to die in battle (though it is also likely he knows they can take care of themselves).
A young James Shiba believed that boxing was the strongest martial art, as he mastered the martial art as a professional boxer and participated frequently in underground bouts for years to prove it's superiority against other martial artists and fighters. In some undetermined time during these years, Shiba met and began a harmless but rather unfriendly rivalry with Akisame Koetsuji. How and why this happened is currently unknown.
As his boxing career continued, Shiba maintains his beliefs within the underground world and ultimately becomes an undefeated champion in the process. Though he manages to make a name for himself quickly and conveniently, everything crashes around him when he loses in a fight with Saiga Fūrinji, which leaves him with a crippled right leg and a permanently damaged right eye. Due to these injuries, Shiba was forced to retire from the ring, supposedly making him die as a martial artist and laying him to waste as a fighter for several years. However, it is later revealed that the "Saiga" he fought was really the leader of the Kuremisago Clan, Senzui, as the real Saiga is still possibly a Kasujinken.
While being a former boxing champion who was famous within the underworld gaining the nicknamed "The God of Destruction", Shiba is a very powerful Grandmaster. While he hasn't fully shown the full potential of his skills as it's unknown since it's yet to have been shown how strong he was in his youth before his loss against Senzui and having his right leg and eye damaged. However, even Akisame has acknowledged his skills for Takeda to train under him and has shown to be a force to be reckoned with nonetheless. Despite being inactive martial arts world for years, Shiba has proven himself to be an incredible master-class fighter, this was proven during his encounters with Senzui. Despite losing his first fight with Senzui years ago leading to him losing his right eye and damaging his left leg, Shiba has continued to pursue him, and despite still being greatly outmatched by him, Shiba has become able to at the very least graze him with one his attacks, something with which Senzui was very impressed by.
- Master Boxer: James Shiba is a Grand Master martial artist, and one of the very few Master class boxers in the world, something that was stated by both Takeda Ikki and Akisame Koetsuji. During his prime, James Shiba was a dangerously powerful master class boxer within both the regular and underground boxing world. Shiba even managed to conquer the underground world of boxing as the undefeated champion till his defeat at the hands of "Saiga Furinji". Even after retiring due to his leg and eye injuries, Shiba maintained his skills as a master, and is still more than capable of keeping up with masters like Akisame and Shigure, and fighting against Yami masters like the One Shadow Nine Fists and the Hachiou Executioner Blade.
- Immense Speed: Despite being somewhat rusty, Shiba has displayed considerable speed to the point he was able to dodge all of Shigure's slashes at him and even keep her from being able to catch up with him. Thanks to his right leg having a spring in it, Shiba is able to jump much higher than most masters. Even against his rival Akisame he's able to run at such a speed that even Akisame was left even in terms of speed. His speed also extends to his jumping capabilities, as he's capable of jumping up 20 floors while holding Niijima to escape.
- Immense Strength: Shiba has great strength enough to take Takeda out with one blow when training him. Even against several thugs Shiba was able to hold back and knock them all out with one blow. His punches alone can create powerful air pressures along with destroying multiple sections of a concrete corridor in order to cause a cave in that would hinder Senzui when sending Niijima to the control room to deactivate the missile during the Eternal Sunset.
- Immense Durability: Shiba has shown to be a highly durable fighter, capable of taking numerous blows from Senzui, the leader of Yami and the head of the Kuremisago clan, and rise continuously during their struggle before succumbing to his wounds.
James Shiba is first seen coming out of a Pachinko parlor and being assaulted by a group of thugs. He effortlessly defeats them, and pummels Takeda after the latter tries to approach him. For two days, he doesn't come out of his shack, waiting for Takeda to leave while the Shinpaku captain waits at his front door. He does come out after Kenichi mentions Koetsuji's name, though takes this opportunity to steal the wallets of the two Shinpaku members. Seeing Takeda's persistence, James attempts to get rid of him by having him first find a supposedly non-existent two headed pachinko ball (which he found nearby, having been dropped by chance); then run to the sea while dragging a tire, find a rare breed of fish and sea slug, and then sing Tan-Tan-Tanuki while doing a hundred Hindu squats at a police box on the way back, (he found the fish and sea slug on his first try, the police cheered him on (as opposed to James's intent to get him arrested), and an old woman gave him a bento), all of which he passed. Despite this, James was still hesitant to take Takeda as a disciple, claiming he was only a shadow of what he was before, but upon hearing that Yami was involved and that he and Takeda had the same left straight best punch he agrees to train Takeda, noting he finally began to feel his boxing spirit arising again, believing that the meeting between him and Takeda was fate.
James is shown later arguing with Koetsuji in a mustache feud, with the two pitting their disciples against each other and betting that the losing disciple's master must shave his mustache. Watching Takeda, James's demonstrates the fruits of his teachings as Takeda puts up a very strong fight against Kenichi, but right as Takeda is about to be finished off, James throws in a towel and forfeits the match, forgetting about the bet to cut off his mustache and blatantly refusing when reminded of it. However, as Akisame takes pity on him about it and decides to forget the bet, Shiba angrily grabs the razor and shaves off only a small part of his mustache and laughs while running away and Akisame yells his name in anger. He is chased by Shigure while Akisame tells her to "shave all the hair off of his body" for not shaving all of his mustache off and Shigure calls him a "mustache bastard" for running away.
One night, after coming back from the liquor store, Shiba sees Takeda, Freya, Kisara, Ukita and Shiratori all out on the town having just left a karaoke bar together. He then notices that he's been followed by assassins from a criminal organization he owes money to. Shiba decides to take advantage of the situation and punches a thug sending him flying towards his disciple. He considers the gesture a "stylish gift" to Takeda; it's a way for his student to show his mettle and fighting prowess to impress the girls he is with. The rest of the thugs attack the youngsters and Shiba himself is impressed with how capable Kisara, Freya and Shiratori are in the fight. The next day, during yet another grueling training session he is giving to Takeda, they run into Kenichi, Miu and Ukita discussing his upcoming fight against Shiratori. Shiba bluntly declares with certainty that Ukita will lose. He informs them that the world is split into types of people: "Those who wait" who are blessed with talent and will always have the advantage and "Those who don't wait" that naively believe that putting forth enough effort can overcome such talents. He points to Miu as someone with talent, Ukita as someone without and Kenichi as a rare exception; a talentless "Bug" that goes against the theory and inspires others to dream the impossible. Takeda tries to defend Ukita by saying his constant training is what has brought him this far but Shiba reprimands him with a punch and tells him just like Shiratori he is another one with actual talent. Before leaving with his disciple to train some more, Shiba states that people should embrace who they are and not try to be anything more or less.
The day of the fight James is proven right when on the roof of the school Shiratori easily defeats Ukita as Kenichi, Miu and Kisara look on. A man working for the organization Shiba owes money to then shows up and accosts the teenagers with a gun intending to kidnap one of them to use as bait to lure James out. Wanting to protect Kisara, Ukita tackles the gunman sending them both flying off of the roof. It's then that James Shiba makes his appearance having been secretly watching the proceedings. On a lower floor, he punches out the windows and catches the falling Ukita, who is still clutching the gunman. Impressed with his guts, he declares he wouldn't expect anything less from a friend of his disciple. He takes Ukita to Ryozanpaku so that Akisame can heal him fearing that his injuries were more severe. Akisame glowingly praises him for his actions believing he's becoming a better person but his mood changes after Shiba reveals he was actually responsible for what happened. Angered that Shiba would endanger the youngsters by putting them in the middle of his shady activities, he goes after the boxer intent on teaching him a lesson. While Akisame pursues him, Shiba runs into Miu in the hallway and is surprised to see that her Ki has awakened. After taking some tea from a tray she was holding, he is eventually cornered by Akisame in a room containing the sculptor's Momimomi statue and threatened to harm it forcing the Jujitsu master to back off. Shiba then scolds Akisame for his hypocrisy arguing that in comparison with what he did, the Ryozanpaku masters put Kenichi in more danger by introducing him to the world of martial arts. Kenichi corrects him stating it was his own choice as he is on this path to protect those he cares about. Shiba calls him naive before jumping out a window breaking one of the statue's arms in the process and running away to escape Akisame wrath.
Later he is seen with Akisame Koetsuji, Shio Sakaki, Apachai Hopachai, Kensei Ma, Kagero Sai, and Danki Kugatachi preparing to rescue Shigure Kosaka. However, he didn't fight the enemy soldiers and told Akisame that his target is just one person while putting his hand on his eye patch. After confronting several of the Yami masters, James, along with the other masters, engages battle with Yami. After Edeltraft splits the masters up, James is seen engaging Ogata. According to Ogata, Shiba has been "gone for a long time", much to Akisame´s chagrin.
Shiba later appears just in time to save Niijima from getting killed by Saiga as requested by Kenichi. However, Shiba says that he did not arrive to save Niijima but rather to settle his grudge against Saiga as Saiga calmly comments that the forgotten underground boxer will die a pointless death.Saiga charges towards Shiba but the boxing master moves back and suddenly grabs Niijima. Saiga is caught off-guard as he realizes that Shiba is taking Niijima to escape. Shiba jumps 20 floors to take Niijima to the missile control room and he laughs at Saiga, saying that he intends to get back at him any way that he can, adding that revenge is about stopping your opponent's goals rather than defeating them in a fight. Shiba drops off Niijima and tells him to go on ahead as he holds back Saiga, destroying the entrance to the hallyway to prevent pursuit. Saiga arrives and mocks Shiba's attempt at buying time as the two masters prepare to fight.
The battle between James Shiba and Saiga Furinji seems to reach its conclusion, with Shiba inside a large crater pressed against the wall. Saiga calmly asks if the fight is over and turns away but Shiba regains his composure and charges towards Saiga, who blocks Shiba's punch with only two fingers and strikes back with a flurry of blows. Saiga compliments Shiba as his attack managed to graze Saiga's hair and he resumes communication with Mikumo. Saiga tells the missile control room to start the countdown and missile silos open as they prepare to launch a missile strike in ten minutes. Shiba gets up once again to fight back but he is easily knocked down and his thoughts go to his disciple Takeda, encouraging them to stop Saiga's plan.
It turns out that Shiba was fighting Senzui disguised as Saiga which means that the leader of OSNF is in fact Senzui all along and that both Hongo and Shiba were defeated by Senzui as oppose to Saiga.
Once the fight was over, Shiba was being treated (albeit reluctantly) by Akisame, but was denied smokes.
In the epilogue, Shiba continues to train Takeda and now at times Freya. However, he needs crutches now to get around due to his wounds from Senzui. He is now enjoying teasing his disciple in his relationship with Freya despite the two denying anything serious.
- Vs Akisame Koetsuji (Lost, Akisame tells this to Takeda in the Anime only)
- (presumed) Vs Senzui (posing as Saiga Furinji) (Lost, received a damaged eye and lost a leg)