Aizawa became extremely ill and had to leave, so everyone would have a substitute teacher

Deku: I hope the new teacher is nice

Urakaka: Yes, but I wish Mr. Aizawa well

Bakugo: Hmph May the New Teacher Don't Disturb Me Like Aizawa

Todoroki: If You Don't Disrupt Every Class

Momo: Enough, you two, give a good impression to the new teacher

The New Teacher Arrives Walking Calmly Into the Classroom, Turning to the Class

Cynthia: Hello, Good Morning Everyone, I'll Be Your New Teacher