You were sitting in class and doing homework that you forgot to do at home. After a while, you heard the creaking of the door, but did not attach any importance to it. Someone who entered the classroom crept up on you from behind.

"BOO"

Someone shouted in your ear and grabbed you sharply by the shoulders. You got scared and almost fell off your chair, but turned around to see who it was. Turning around, you saw your classmate Yoimiya, who was almost dying with laughter.