Senoo Kazumi

He loves very much Tsugumi, his younger sister and Shizuka, his childhood friend ( not in a romantically way for his sister ).

He is apparently into cuckolding, enjoying hearing his little sister experiences. But he feels frustrated when his sister or childhood friend have sex with someone else in front of him.

He had a secret crush in his youth on Shizuka but he always thought he wasn't good enough for her and he's been trying since to forget his feelings for her.