Hosu Incident

TheHosu Incident (保須事件) is an event that takes place during the Unforeseen Simulation Joint Arc.

Prologue
After killing seventeen heroes and injuring twenty-three beyond recovery, Hero Killer: Stain becomes a scourge on the hero community. The Turbo Hero: Ingenium and his squad search for Stain in Hosu. Ingenium eventually finds Stain in an alleyway and confronts the villain. The Hero Killer manages to grievously injure Ingenium and leaves him for dead.

The news of the attack draws the League of Villains to Stain. They approach him on the roof of a building and invite him into their hideout. Tomura Shigaraki asks Stain to join their party. Stain asks for Tomura's motivations and is deeply disappointed with the answer.

The villains come to blows, Stain paralyzes Kurogiri, then stabs Tomura and pins him to the ground. Stain tells Tomura that he's weak because he lacks conviction. Tomura destroys Stain's knife and forces him back. He tells the Hero Killer that he desires to destroy society because it praises All Might. Stain realizes that they both agree to destroy the present. Tomura demands he leave and Stain explains he attacked him to test his motives. Kurogiri is freed and he agrees to return Stain to Hosu.

Tomura and Kurogiri follow Stain to Hosu. Tomura asks Stain what he plans to do there. Stain explains he must spill blood in order to reform it. Kurogiri commends his efforts. Stain goes on to say that hero is a title for great champions, not people who desire glory and payment for their heroic deeds. Then he jumps into the city and continues his work. Tomura claims that Stain is wasting his time, but Kurogiri argues that Stain has positively affected all the cities he's appeared in.

Irritated, Tomura mocks Stain and claims he can never work with the Hero Killer. He requests three Nomu's from All For One and has Kurogiri warp them to Hosu City.

Incident
The Nomu attack the city by destroying buildings and assaulting civilians indiscriminately. Heroes mobilize to the site of the chaos. One Nomu attacks a nearby train, which happens to harbor Izuku and Gran Torino. Gran Torino tackles the Nomu off the train and saves the Pro-Hero it was attacking. Izuku exits the train to search for Gran Torino. Manual takes Tenya towards the center of the incident, but the young man veers off the path to confront Stain.

The Hero Killer finds his next target in the Pro-Hero Native. He paralyzes Native and prepares to kill him. Tenya intervenes and rushes Stain, but the villain counterattacks and slashes Tenya's helmet off. He tells the child to run away, but Tenya declares that he will avenge his brother. Stain is displeased with Tenya's search for vengeance and decides to make him a target of his purge.

Izuku uses One For All: Full Cowl to jump through rooftops and search the city for Gran Torino. The Nomu Gran Torino's fighting recovers and attacks nearby civilians. Gran Torino stops him with the help of Endeavor. The citizens of the city frantically evacuate while Izuku continues running through the streets in search of Gran Torino. He realizes the entire city could be in trouble if this Nomu is like the one from the USJ Incident.

Izuku notices Manual's voice calling for Tenya and happens upon a scene where two more Nomu are dominating Pro-Heroes in a fight. Manual helps put out the fires caused by their destruction. Izuku overhears him talking about how Tenya went off on his own. One of the heroes tells Izuku to evacuate and then he realizes that Tenya likely encountered Stain. Izuku leaves while the Nomu continues to defeat the Pro-Heroes.

Izuku surmises that the League of Villains and Stain are connected. He searches the back alleys of Hosu, looking for Stain far away from the chaos because Stain normally operates in the shadows. Izuku successfully finds Tenya and the Hero Killer just in time to save the former from death.