Shuuji is an employee at Koigakubo and works as Himeko's bodyguard.
He goes to Himeko's school but is younger than her.
He hates violence and wants to destroy violence. Using Himeko who falls in love with violent people he tries to fulfill this wish.
He has an older sister. Their parents got abusive and constantly beat the two of them up due to stress. His sister always protected him. Then his sister killed their parents and committed suicide right after.
This is probably also the reason why he hates violence and wants to eliminate it.