Kendo Rappa/Synopsis

History
Kendo used to spend his days fighting in underground fighting rings. He did this as a rebellion over his strict parents. In that fight club, fighters could go berserk with their Quirks. Kendo's battle prowess made him too powerful for all his opponents and he never got the death-match he always desired.

One time Kendo, under the name "The Rapper", participated in the Underground Masquerade an underground fighting event that took place in Osaka. There, he was matched against The Ripper, who was the pro hero O'Clock in disguise. Kendo complained that their names sounded similar, and because The Ripper had a knife in his hands. Kendo explains that he thinks a real fight shouldn't involve weapons, but Ripper claims that the knife levels the playing field.

Once the bell is rung, Kendo sends a barrage of punches at Ripper, who is using his Overclock Quirk to make it seem he is barely dodging the attack, and drops his knife and mask in a way that seemed natural. Ripper gets up and declares that he will fight by Kendo's rules, delighting him greatly. He continues attacking Ripper, who keeps up with Kendo's speed, until Ripper feigns getting hit by Kendo since he didn't need to be in the ring any longer. The announcer declares Kendo's victory, and the "unconscious" Ripper is taken to another room.

Feeling that something wasn't right, Kendo heads for the sick bay, where he sees The Ripper leaving. Kendo gives him half of his prize money, along with the bonus, because he realized that The Ripper didn't put his heart into the fight and went down easily, so it didn't count. He gets excited for a rematch to the death, but Ripper swiftly declines. Kendo points out that Ripper loves to take part in fights like this, but Ripper denies, saying that he prefers one-on-one sneak attacks over long, drawn-out fistfights. Kendo states that they had fun in the ring, but Ripper claims that was just for show, and that it's the first and last time he'll take part in something like that. Kendo tells him that life is not fun without a little recklessness, and that the soul decides hate and love, recognizing that even if The Ripper doesn't admit it, deep down he loves that stuff. Just then, The Ripper starts to hear loud noise seemingly riling up the crowd down in the arena.

At some point, Overhaul attended the underground fight club to recruit Kendo to the Yakuza and challenged him. Kendo accepted the challenge but during the combat he "died" at the hands of Overhaul, who used his Quirk to deconstruct Kendo's upper body, just to be repaired a few seconds later.

Having suffered in his own flesh the power of Overhaul, Kendo had no choice but to agree to join the Shie Hassaikai. However, he holds a grudge against Overhaul, and has challenged him to fight up to five times, only to being defeated in each and every one of them. Since then, he has followed Overhaul's orders but has no loyalty to him.

Shie Hassaikai Arc
During the raid of Overhaul's hideout, Kendo is paired with Hekiji. When Joi Irinaka launches Fat Gum and Eijiro into another room, Hekiji and Kendo are already waiting for them. Launching a barrage of punches, Kendo manages to break through Eijiro's Red Riot Unbreakable. Taishiro tries to punch Kendo, but Hekiji protects his partner with a Barrier.

Kendo complains when Hekiji stops him from attacking Taishiro, to which Hekiji reminds him that Overhaul paired the two up because their Quirks have great synergy. Kendo replies by trying to attack Hekiji, which he blocks with his Quirk. A confused Hekiji asks Kendo what he is doing, to which Kendo replies that he does not care about Overhaul's plans and that he only wants to kill. Hekiji decides to let him do as he pleases, while also reminding him to address Overhaul properly.

As Taishiro prepares to fight back, Kendo orders Hekiji not to interfere, to which Hekiji assures him that he will not. Upon seeing Eijiro's fear, Hekiji notes that he has already given up and expresses pity for the young hero. After Kendo is done assaulting Taishiro, Hekiji notices that Taishiro is preparing for another counterattack and tells Kendo to finish things quickly.

As Kendo tries to finish Fan Gum off, Eijiro interferes, taking his attacks and attempting his own counterattack; however, Hekiji blocks it with a barrier. Hekiji simply notes how meaningless it was for Eijiro to take these attacks.

Soon, however, he realizes that Eijiro's actions were not in vain as Taishiro emerges from the dust and releases all the impact he stored from Kendo's punches with a single powerful blow. Hekiji however creates a barrier with maximum defense that absorbs most of the impact, which prevents the two from being knocked out. Kendo stands up again and claims that it is a fight to the death and he is not dead yet.

Fat Gum gets nervous because he is not in a position to continue the fight, but to his surprise, Rappa asks Fat Gum to take Eijiro to the next room with first-aid supplies, where he can treat their wounds. Fat Gum questions about it being a trap, but Rappa denies it. Hekiji questions the selfish attitude of Kendo and demands that he follow his orders, but Kendo knocks out Hekiji by stomping on his chest and declares that he wants a fight to the death against Eijiro.

Fat Gum moves Eijiro to the first aid room, where he bandages him, managing to stop his bleeding. Seeing that they are opening up to each other even though they are on opposing sides, Fat Gum asks about the reason Kendo is following Overhaul. Kendo explains that he is only around to defeat Overhaul someday, because he has been the only one who has defeated him not once but several times and always without difficulty.

After hearing his explanation about Kai Chisaki, Fat Gum becomes concerned and proceeds to ask Rappa about Chisaki's plans. Kendo tells him that Overhaul wants to reinstate the Yakuza, although Kendo doesn't know exactly how.

After Kai's defeat and Eri's rescue, he was apprehended by Centipeder and arrested.