K'

3rd year high school student.
The protagonist's childhood friend, but he moved away after elementary and they've grown apart.
They've met again and are in the same class, but he's turned into a delinquent who doesn't show up at school often.
He gets really mad when he's called "K-kun".
He hangs out with a gang of delinquents who apparently do some bad things.
He has a middle school aged younger sister named Kuura.