Kousuke Oosiba

A teacher, and gang fighter, Kousuke spends his days as a temp math teacher at Masahiro, Asaya, and Kensuke's school and can occasionally at night be found fighting street gangs known as the "Bear Killer." He is Kensuke's older brother, and has a soft spot for his brother's best friend Masahiro Setagawa who he soon admits to have feelings for. He has to protect Masahiro from his old gang, due to Masahiro leaving without stating anything to the leader.