Katana Man/History

History
When he was younger, Katana Man was spoiled by his Yakuza grandfather, who fed him good food at expensive restaurants and bought him anything he wanted with drug money. At some point in the present, he learned that his grandfather was killed by Denji. Katana Man then swore revenge on Denji, believing that the latter was responsible for his grandfather's death. However, he doesn't seem to realize that it was actually the Zombie Devil that took the old man's life.

To these ends, he formed an arrangement with Akane Sawatari, in which she replaced his organic human heart with the Katana Devil's heart. This allowed him to transform into a Hybrid, and with that, Katana Man and Sawatari began plotting their attack on Denji and his allies from Special Division 4.

Katana Man arc
During the Yakuza's attack on Special Division 4, Katana Man ate at the same restaurant as Denji, Aki, Himeno and Power. He commented that the food was disgusting and went into a speech about refined taste and how a person's upbringing will affect them. As the others considered leaving instead of responding to him, he brought up his grandfather and showed Denji a picture of the Yakuza boss that Denji worked for in the past.

Before Denji could react, Katana Man pulled out a pistol and gunned down Denji, Himeno and Aki. Power swiftly moved out of his sight and hit him with an uppercut to knock him back. Aki then follows up by summoning the Fox Devil to swallow Katana Man whole. However, Katana Man transforms into his Hybrid form, proceeding to slice his way out of the Fox Devil before crashing down to face his opponents.

Aki draws out a spike with a sword hilt and engages Katana Man. Katana Man is stabbed three times in a row by Aki which summons the Curse Devil. The Curse Devil grabs Katana Man and violently kills him. Akane Sawatari appears in the ruined building and crouches down near Katana Man, reviving him. As Aki watches in shock, Katana Man tells Sawatari that he underestimated his opponent, and prepares to use his special technique. Crouching down with his blade arms at his side, Katana Man dashes forward with his blades outstretched, creating a large tear through Aki's chest that fatally wounds him.

Before Katana Man can finish off Aki, Himeno intervenes by using the full power of her Ghost Devil to overwhelm him. Unable to effectively fight back, Katana Man begs Akane for assistance and she uses her Snake Devil to swallow the Ghost Devil while Himeno's body vanishes. In her final moments Himeno pulls Denji's chainsaw cord to revive him. Katana Man and Denji charge at each other as Katana Man swears he'll put Denji down a second time.

Katana Man and Denji clash multiple times, destroying the building around them. Later on, Katana Man's subordinates arrive to back him up and he tells them to aim for Denji's arms or his heart. Denji takes one of them hostage but Katana Man uses his dashing technique again to blitz Denji at high speed and cut through both Denji and the hostage. With Denji bisected and defeated, Katana Man's transformation became undone and he reverts to his human form while declaring victory over the Devil Hunters who can't stand up to the power of guns.

Katana Man and Akane lead their people outside to a van that they're trying to load Denji into, but suddenly his subordinates start dying around him. Akane tells him that they should escape while they still can, and that it is likely that Makima herself is attacking. Cursing, Katana Man tries to pick up Denji but notices Kobeni approaching them. Akane tries attacking her with the Snake Devil but Kobeni nimbly avoids the attack and runs across its body towards them. He tries gunning her down but Kobeni cuts off his arm and catches his gun, shooting him twice in the back. When Kobeni runs out of bullets Akane escapes after throwing Katana Man's body inside the van.

Kishibe tells Denji and Power that their first mission of real combat will be to capture Katana Man and his accomplice Akane. At his hideout, Katana Man fumes over Denji and tells his underlings that he won't run away, just like how his grandfather wouldn't. Akane tells their subordinates not to worry about their boss since even if he dies he will be revived. As the two head over to face Public Safety, Akane tells Katana Man that they'll kill as many devil hunters as possible and try to steal Denji's heart if possible before escaping through the Snake Devil. Katana Man swears he'll kill Denji, while Akane tells him not to lose his cool.

During the raid on Katana Man's hideout, Denji took the elevator by himself after Power disembarked to fight some zombies and he encountered Katana Man with a couple of his subordinates. Instead of fighting right away Katana Man offered depending on Denji's attitude. He demanded that Denji allow himself to be killed without resistance in order to satisfy the Yakuza's anger, but Denji refused leading to both of them transforming at the same time. Katana Man charged at Denji, sending both of them flying through the wall and they clash in the air outside.

Denji lands on a train, followed by Katana Man who knocks him through the roof of the carriage and into the train. Katana Man blitzes Denji twice in quick succession while Denji tries to protect a civilian, leading to both of Denji's arms being cut off. Katana Man demands once more than he apologize for killing his grandfather but Denji claims he can still fight because he has the chainsaw on his head. Katana Man, baited by Denji's words, charges at him a third time and shatters the chainsaw on Denji's head while simultaneously being cut in half by a new chainsaw that Denji sprouted from his legs. Denji calls him a moron while Katana Man falls apart.

After recovering, Denji pulls the arm katana out of Katana Man causing his body parts to stick back together and for him to revert back to his human form. He is then tied up with a chainsaw chain and stripped to his boxers while Denji waits for Aki to arrive. Denji thinks of some way to get payback against Katana Man for shooting Himeno, and as Aki arrives he announces that he will hold a tournment; whichever ones of them gets the biggest scream of pain from kicking him in the nuts wins. Aki is initially reluctant but changes his mind after looking at Himeno's cigarrete which has "Easy revenge!" written on it. The two then take turns kicking him as as their way of paying respect to Himeno.

Bomb Girl arc
Denji recalls Katana Man's method of dashing forwards at high speed and starting thinking about how he could apply his own powers towards mobility as a result during his battle with Reze.

International Assassins arc
Power mentions Denji's fight with Katana Man on a speeding bullet train when it appears on TV alongside some of Denji's other battles with previous adversaries and Reze.

Control Devil arc
Despite being arrested, Katana Man was brainwashed offscreen by Makima to serve her own needs. He is summoned as part of Makima's newly-formed Special Division 5, a team of weapon hybrids created for the sole purpose of battling the fully-powered Chainsaw Devil. While under Makima's control, Katana Man behaves protectively and with great affection towards her.

Once Makima commands Special Division 5 to attack, each member activates their weapon trigger, transforming into their Hybrid forms. They all leap from their respective spots to lunge straight towards Chainsaw Man. Before any of the Hybrids can land a single blow on him, they are all blown back by Chainsaw Man leaping forward from the building he stood on to initiate the fight.

After Chainsaw Man defeats Quanxi and the Longsword Hybrid inside a destroyed building, Katana Man appears behind him and attempts to use his special move like he did with Denji. After moving through his opponent, however, Katana Man ends up being shredded to pieces as Chainsaw Man effortlessly decapitates him without budging an inch.

At some point in the future, Katana Man is revived once more by Makima, alongside the rest of Special Division 5, and brought to a graveyard to confront Denji. Once Makima finishes monologuing her thoughts of erasing anything she dislikes to Pochita (who is disguised as Denji), Katana Man and the other Weapon Humans transform into their Hybrid forms for the final battle. Pochita starts the battle by slamming his fists into the ground, lifting up a huge chunk of the ground to throw straight towards Makima using his whips.

Katana Man and the Longsword Hybrid act first by leaping forward, both slicing the chunk of land and cutting it down into several dozen smaller chunks. However, the two are left vunerable as Pochita falls towards them from behind the debris. Before the two Hybrids can act any further, Pochita swiftly uses his chainsaws to cut them both, defeating them in the process.