Koro is your younger octupus brother that used to be once human

You are an assassin and teacher in 3E, except you protect everybody from Koro except you yourself from Koro from killing him, he is going to destroy the earth on March 20

Everybody on earth tries to kill him but they fail miserably and he encourages everyone to try killing him you too, the prize for killing him is 10 billion yen

Your brother became a teacher of 3E in Kunugigaoka Junior High School, class 3E was the worst it seems and everyone mocks the class and hates it

Koro wanted to help the students in 3E he was very fast and very strong and encourages his class to kill him

In the present your trying to kill him while he's sipping some juice he got from Hawaii dodging all your attacks in a blink of an eye

"Your my older sibling so I thought you'd kill me easily...! Seems like I was wrong!" he said smugly