Hosu is a ward located in My Hero Academia's version of Tokyo, Japan.
It's the main setting of the Vs. Hero Killer Arc.
The Pro Hero Ingenium was known to act in this district, but an attack caused by a mysterious figure left him paralytic, ending his career. Other notable Heroes known to act in this district include Manual and Endeavor.
During a mission in Hosu, Pro Hero Ingenium was attacked and struck down by the mysterious Hero Killer Stain. Tenya Iida was warned about this midway through the U.A. Sports Festival and abandoned the competition to meet his now crippled brother in the Hosu General Hospital.
As Tomura Shigaraki unleashed his Artificial Humans in the district, Izuku and Gran Torino were passing through it by bullet train, until they got attacked themselves. In parallel, Endeavor and Shoto Todoroki were acting in Hosu to stop the Artificial Humans, as well as to confront and capture Stain. 
Tenya was able to find Stain as he acted to kill a nearby hero in an alley. Tenya was no match though, but Izuku and later Shoto came to his rescue, with the trio managing to defeat and capture the Hero Killer.  After the incident, Izuku, Tenya and Shoto recovered from their injuries in the Hosu General Hospital.
- "保須" (Hosu) is a reference to planet Hoth from the Star Wars universe.