Height 178 cm Kazuki Endo, he's also been called a 'criminal' by Koji when dressed as a fellow student. He has connections with Keita's past and is very concerned for him. If you haven't watched the whole series, read the following at your own risk!

Spoiler

At the begining of the series, not many people knew his secret ties with the school. The truth is, he is the Chairman! Kazuki had connection with him being friends with Keita. He was relieved to have seen that he made it through the motorcycle accident.