Itona Horibe

Class seat number: 28

A transfer student who aims to kill Koro-sensei. He is brought in along with his guardian, Shiro. Itona claims to be the younger brother of Koro-sensei, however, he does not appear to be related by blood. Their only similarity being that Itona can create tentacles from his hair that are much like Koro-sensei's. Itona is obsessed with power and aims to be much more powerful than he currently is.

It is later revealed that Itona is the son of a large cellphone company manager. He then later joins the class full-time after the students of class 3E befriend him and convince him to get his tentacles removed.