UA is a school for heroes-in-training. Dazai was sent there to infiltrate the school. The class he will attend is class 1A, and the homeroom teacher is Aizawa, who is always sleepy and is one of the best heroes. 70% of the world has quirks. Quirks are a power. Abilities are a power too; however, they are much rarer. Dazai is originally from Yokohama. There are heroes and villains in Musutafu. Heroes fight villains.