Samejima

Samejima is the leader and the guitarist of the band High and Nothing (High 'n No (ハイエナ) for short), which uses ANTIKNOCK as its home for concert activities.
He apparently has affection for their band's vocalist, Riho.

Because of that, he winds up at odds with Shoichi over Riho's loyalties, but he's not a bad person at heart.