Justice Devil arc

Spanning chapters 98 through 111, this arc follows the Control Devil finale and leads into the Dating Denji story. It introduces the new protagonist Asa Mitaka, her tenant devil Yoru, and the broader Academy Saga cast while reframing Denji as a hidden student.

Asa's homeroom teacher Mr. Tanaka keeps a Chicken Devil named Bucky as a class pet, planning to make the students kill and eat it to teach the value of life. The class grows fond of Bucky and decides to spare it, isolating the resentful Asa further. Trying to make friends, Asa trips and crushes Bucky to death, mortifying herself before the whole class. That night the class president lures her to Bucky's grave, transforms via a contract with the Justice Devil, and slices Asa's face in half, revealing she was ordered to engineer Bucky's death.

A potoo-like bird revives Asa, who rises with a facial scar and reveals herself as Yoru, the War Devil. She turns Mr. Tanaka into a sword, destroys the class president, and vows to make Chainsaw Man vomit up the Nuclear Weapons Devil. Yoru explains that she has left half of Asa's brain intact so the host can blend in, and that Chainsaw Man attends the same school, Fourth East High. Reluctantly, Asa joins the Devil Hunter Club, partnered with Yoshida and a kind girl named Yuko.

Yuko befriends the bullied Asa, lending her shoes and bonding over how devils killed both their parents. Yoru repeatedly urges Asa to turn Yuko into a weapon, but Asa resists the casual violence and the two devils settle into an uneasy pact. When the Bat Devil attacks the girls in town, Denji intervenes, hurling the Cockroach Devil to kill it before saving a cat. Yoshida warns Denji to keep his identity hidden, while Yoru seethes at being rescued.

Yuko confesses she murdered a neighbor and contracted the Justice Devil to protect Asa, then resolves to kill her bullies. The two devils clash at school, and after Yuko slaughters classmates and hunters, Asa forges a Super-Strong Uniform Sword and cuts her apart. A mysterious student, Fami, heals Yuko into a more monstrous form, but Denji ultimately defeats her, and Yoshida teleports him away to stop him exposing himself. That night a trapped Yuko visits Asa to say goodbye, and the two reconcile over the lent shoes before a Chainsaw Man-like figure kills Yuko as she flees. The arc introduces Asa Mitaka, Bucky, Mr. Tanaka, Yoru, Yuko, the Cockroach Devil, Seigi Akoku, Furio, and Fami.