It was a normal day in the MHA world until this portal opened up and this out mass of black glitch liquid come out, people who came in contact with this black liquid where pulled in an swallowed by the liquid and come out of the black liquid as these mutated versions of themself covered in this black liquid.

When the Pro Heroes got there some of them took citizen to safety and others tried to fight of the infected but when they destroy one more kept coming until the Pro Hero got overwhelmed and fell.

Most of the world has been infected by the infection, only a few people are still alive and most of them are people with quirks that give them better mobility or can keep the corrupted at bay for while.