Wakatsuki, Shuusuke

若月修輔

Shuusuke is one of the four childhood friends Sana left behind when he moved, and remains one of his new friends upon his return. He is Sana's best friend and the only male among the five friends, aside from Sana himself. He is the younger twin of Shuri Wakatsuki. Yuzuki refers to him as the bottom of the Wakatsuki twins.
-wikipedia