Transfer Student Time, 2nd Period

Karasuma learns from the Ministry of Defense that a second transfer student and his attendant will arrive, and passes word to Korosensei. Ritsu explains that the pair were meant to work in tandem, the AI at range and the newcomer up close, but the plan collapsed because the two cannot cooperate and the boy far outmatches her. A man in white, calling himself Shiro, then appears as the arrival's guardian, and the back wall bursts open to reveal Itona Horibe, who declares himself stronger than the wall and challenges Korosensei to an after-school fight, insisting they are brothers.

Throughout the day the class notices eerie shared habits between the two, though Korosensei denies any kinship, claiming he was raised an only child.

The classroom is cleared into an arena, the rule being that a fighter loses on crossing the desk boundary, with Korosensei adding forfeiture if a student is harmed. Shiro starts the bout and Korosensei's tentacle is severed at once, shocking everyone less than the sight of Itona's hair writhing with identical tentacles. Exploiting the octopus's weaknesses and a beam from Shiro that slows his reactions, Itona gains the upper hand, but Korosensei has scattered anti-sensei knives to feign being struck, then wraps Itona in shed skin and hurls him outside to win.

Shiro knocks the raging boy out with a wrist device and carries him off, and when Korosensei reaches for Shiro his tentacle hand is destroyed, revealing the white robe is anti-sensei material. Afterward the students, inspired, ask Karasuma to teach them more, no longer content to let someone else do the killing.

The episode adapts Chapters 29 through 32 and marks the debut of both Itona Horibe and Shiro. It first aired in Japan on March 27, 2015.