Izumi Sano is the male protaganist of the series. An excellent high jumper before entering high school, he stopped for personal reasons when he entered high school. He found out Mizuki's true gender due to an accident early in the series. He didn't tell anyone else about Mizuki and becomes protective of her due to her secret.
Before Mizuki's arrival, Sano had been injured in an accident when he saved his team captain from being hit by a car, causing him to quit high jumping for a while because he thought that he couldn't handle the pressure. Sano later falls in love with Mizuki, but couldn't tell her of the fear that she would have to leave if she knew her true gender was made known.
In the last chapter, he followed Mizuki to California, pursuing both his college and high jump career at UC Berkeley. He eventually is able to confess his feelings for her. He proposes to Mizuki at the end of the series.
an extended description!