The Katana Man Arc is the 4th Arc of Chainsaw Man which takes place from chapters 23 to 39. The arc follows the Special Division members as almost all of them are attacked and killed by henchmen of the Gun Devil.
Simultaneously, Denji, Power, Himeno, and Aki are eating in a restaurant when they meet the Katana Man who tells Denji the story of his grandfather who he loved deeply and also shared a relationship with Denji earlier before Denji killed him.
Following this, he shoots Denji in the head and aims at the others as well. Aki uses the Fox Devil in an attempt to stop him but Katana Man transforms into his Hybrid Form and escapes.
Aki then proceeds to fight him and even manages to use the Curse Devil which should have been the finishing blow but a woman called Sawatari suddenly appears and revives Katana Man who then cuts Aki down.
Having been shot earlier, Himeno gives herself completely to the Ghost Devil in a bid to stop Katana Man. While she was winning, the combination of Katana Man and Sawatari’s Snake Devil was too much to handle and she ends up being killed with just enough time left to pull Denji’s cord which transforms him into Chainsaw Man.
In the battle between the 2, Katana Man is victorious as he slices through both his opponent and allies. At the same time, Makima conducts a sort of sacrificial ceremony in Kyoto where she uses the life of convicts in exchange for crushing the Gun Devil’s henchmen with an invisible force.
Due to this confusion, Kobeni manages to save Denji from Sawatari and Katana Man. Following this, Denji and Power visit Aki in the hospital as he mourns Himeno’s death while Denji wonders if he is capable of feeling such emotions.
After these chaotic events, Denji and Power are introduced to a devil hunter called Kishibe to be trained by him while Aki makes a contract with the Future Devil to get even stronger.
On the other end of the spectrum, Sawatari and Katana Man were preparing a horde of zombies for their attack against Special Division 4. However, things are not as catastrophic as last time for the devil hunters as they easily defeat the zombies with the shark fiend, violent fiend, and several other devils.
Aki attacks Sawatari who uses the Ghost Devil she had taken from Himeno, however, using the various skills and devil powers at his disposal, he manages to overcome her before Kobeni captures her with a knife. This puts Himeno’s soul to rest completely while offering some peace of heart for Aki.
The final battle of the arc is the rematch between Chainsaw Man and Katana Man. While Denji was easily defeated the first time, the results this time were the complete opposite. Using his quick thinking and adaptability, Denji slices straight through Katana Man and defeats him. In a bittersweet ending to the arc, we see Denji and Aki kicking Katana Man in his human form together while further deepening their bond.