Chapter 51: No, Knock It Off, Ida

Izuku Midoriya leaves the train at a run, aiming for Hosu City and the fight Gran Torino is already in. The elderly hero has driven the Nomu-like creature through a small building; when it swings at him he slips the blow, then spots it turning toward two civilians. His counterattack is cut short by a wall of flame. Endeavor, who set the creature alight, notes that the two of them have never been introduced and claims the kill for himself.

Arriving in the city proper, Izuku finds professionals trading blows with a second pair of the creatures, and no sign of his classmate anywhere in the chaos. The absence tells him everything: Tenya came here hunting the Hero Killer. He abandons the battlefield to search. Above the streets, Tomura Shigaraki compliments his three Nomu on the destruction. Kurogiri asks whether he intends to join in, and Tomura begs off on account of his injuries, predicting that by sunrise nobody will remember Stain at all.

The duel Tenya wanted goes nowhere. His opening kick, fast as it is, gets read and hopped over. Stain lands a strike on his right arm hard enough to draw blood, drives him into the pavement underfoot, and skewers his left shoulder with a katana. Then comes the part that hurts more: Stain admits he spared Ingenium deliberately, letting the survivor feed the legend, and dismisses both brothers as counterfeits. Tenya, broken on the ground, still defends Tensei as a splendid hero and swears he will kill Stain for him. Stain answers by pointing at the wounded professional lying nearby and telling Tenya to go save him.

The lecture follows. Rescue comes before ego, Stain argues, and vengeance dressed as heroism is the furthest thing from the title, which is why the boy has to die. A boot presses down on Tenya's head and the katana rises to make the boy a tribute to the fair world Stain imagines. Tenya refuses the sermon outright, calling his executioner nothing but scum who maimed his brother. The blade never falls. Izuku arrives with One For All running through his whole body and buries a fist in Stain's face, announcing that he has come for Tenya.

Nomu tear through Hosu City on multiple fronts, drawing the professional heroes into a scattered defense.

Endeavor turns up in Hosu, and his reason for being there is the Hero Killer.

Stain confirms that Ingenium was left alive on purpose, as fuel for his own reputation.

Izuku locates Tenya and stops the killing blow at the last moment.

The chapter marks the debut of The Fly and was adapted as episode 29 of the anime.

It ran in issue 34 of 2015, dated July 20, 2015, and was collected in volume 6 across twenty-one pages. Gran Torino and the Four-Eyed Nomu share the cover, and a sketch version of that art also survives.

Kohei Horikoshi used his author comment to celebrate the series landing its third magazine cover, calling the news dreamlike.