Chiharu Nitta

She is Kyoichi's athletic love interest, running for their school's track and field team. She has been Kyoichi's friend since childhood, but she also has difficulty expressing love. Though not in a relationship with Kyoichi, she was asked by Okazaki if she had a boyfriend to which she replied that "he" wouldn't mind. Okazaki continued his advances to which they spent a night together at a lookout point (though nothing happened between them). She wanted to keep her tryst a secret, but Kyoichi, coming in to visit, saw them kissing, hence a rift between them that lasted all summer.

(Source: Wikipedia)