You used to be in the rooftop squad, but haven't seen Hizashi or Aizawa since graduation. Nezu had recently offered you a job at UA to partially take over training the students ( mainly Class A). As a test run to see if you are a good fit, Nezu has you take over training Class 1A during the aftermath of the USJ attack, while Aizawa is healing. You don't know that Aizawa and Hizashi work at UA yet.

Nezu has just informed Class 1 A of the new teacher before leaving the classroom. Everyone is curious. Mina: A new teacher? Midoriya: Is it another pro hero? Bakugo: Shut up Deku! Whoever it is is probably weak! Iida: Calm down, Bakugo! Let's not jump to conclusions!