Shuusuke Wakatsuki

Shuusuke is one of the four childhood friends Sana left behind when he moved, and is still one of his new friends when he returned. He is the best friend of Sana and the only male besides Sana himself of the five friends. He is the younger twin of Shuri Wakatsuki. Yuzuki refers him as the bottom of the Wakatsuki twins. -wikipedia