Katsuma Shimano

Katsuma is gentle, shy, and considerably less confrontational than his older sister. He tends to follow Mahoro Shimano and initially lacks the confidence to openly defend his desire to become a hero when she discourages him. His admiration for heroes is sincere, however, and he keeps an Edgeshot pin among his possessions.

His experiences with Izuku Midoriya strengthen that aspiration. Even while frightened, Katsuma demonstrates courage when people he cares about are endangered, and he refuses to simply abandon others when doing so would conflict with his idea of heroic behavior.

Cell Activation is an Emitter-type Quirk that allows Katsuma to stimulate the cells of another person through physical contact. It accelerates recovery from injuries and can improve the recipient's physical condition. Prolonged use consumes Katsuma's stamina, leaving him exhausted after extensive healing.

His version is notably more versatile than his father's similar Quirk. Whereas Mr. Shimano's Cell Activation is restricted by blood-type compatibility, Katsuma demonstrates compatibility with several blood types. During the battle for Nabu Island, he uses it to restore Izuku Midoriya and Katsuki Bakugo after their injuries.

Years later, Katsuma enrolls in U.A. High School's Hero Course, showing that his childhood ambition eventually develops into formal hero training.

Katsuma first meets Class 1-A during its temporary hero work on Nabu Island. His admiration for heroes contrasts with Mahoro's distrust of the profession, and Izuku encourages him rather than dismissing his ambition. The siblings soon become central to the conflict when Nine's group targets their family.

Nine seeks a Cell Activation Quirk capable of counteracting the deterioration of his body. After stealing the version possessed by Katsuma's father and discovering that it is incompatible with his blood type, Nine realizes that one of the man's children may possess a suitable variation. Katsuma consequently becomes his primary target.

Katsuma assists the students despite being unable to fight Nine directly, most importantly by treating Izuku and Bakugo after their first confrontation. After the battle, Izuku reassures Katsuma that he can become a hero, echoing the encouragement All Might once gave Izuku. Katsuma later appears as a U.A. Hero Course student.

Mahoro Shimano is Katsuma's older sister and closest family companion on Nabu Island. She is highly protective of him and initially discourages his hero ambitions because she fears the dangers involved. Katsuma nevertheless trusts and loves her, while their experiences with Class 1-A gradually challenge her view of heroes.

Izuku Midoriya becomes Katsuma's most important heroic influence. Katsuma admires Deku's willingness to protect people regardless of personal danger, and Izuku treats his ambition seriously rather than viewing his timid personality as an obstacle.

Katsuki Bakugo has a rougher manner around the children, but he repeatedly places himself in danger to defend them. Katsuma later uses Cell Activation to help both Bakugo and Izuku recover from their injuries.

Nine targets Katsuma because of Cell Activation, turning the boy into one of the principal objectives of the villain's attack on Nabu Island. Nine's pursuit also forces Katsuma to confront danger far beyond anything he had previously experienced.