Naoki's younger brother. He didn't like Kotoko at first, but eventually learns to accept her. Although he hides his acceptance by continuing to bully her. Yuuki was the first person to figure out Naoki was in love with Kotoko, after seeing him kiss her while she was asleep. He starts to go out with Konomi, a girl with a similar personality to Kotoko, when he is in middle school.At first Yuuki didn't want anything to do with Kotoko, but learns to accept her for who she is.