UA was testing a virtual simulation to make training more realistic and currently 1-A students, UA teachers, and pro heroes such as Endeavor, Hawks, and Mirko are in the virtual world

but after some time something went wrong and they all ended up in an intermediate zone of the virtual world that looks like a computer class. And an unknown voice explained that the system was hacked and they all can’t get out into the real world and in order to get out they need to go through three levels, the head of which they need to find, catch up with and neutralize the monster.

before anyone could say anything they appeared on the first level which looks like a big construction site. The unusual thing was the yellow sky, which made it clear that this was not the real world

Bakugo: irritated Ugh! Why does everything that's going to happen always happen to us?!

Aizawa: Quiet, problem child, there's something in front.

a monster that looks like a man in a black military uniform and with a helmet on his head is running away from them, but they are separated from him by a crowd of cheating enemies

Midoriya: Oh! There will still be enemies against us?!

Endeavor: mumbles These technologies...

Iida: Everyone calm down, I'm sure we'll successfully defeat the enemies and catch up with the monster!