Rikujoubu no Bokukko Doukyuusei ga Chuunen Komon ni Mesu ni Sareru Ichibu Shijuu

Toshimitsu Fukuyama, a second-year track and field club member, is acquainted with Yuki Hojo, a second-year student of the same age. They call each other "Toshi" and "Yuki" and are rivals in sprint race where they compete for the first place. However, both Toshi and Yuki are aware of each other as a man and a woman, and want to move beyond their previous relationship as "ordinary friends". At the same time, Yuki is confused by the sudden onset of secondary sexual characteristics during puberty, and her body has grown into one that is not suited to sprinting. Her sprinting ability also declines, and Toshi, who is more than a friend but not a lover, begins to think of her as a "woman", causing strain in their relationship, and they eventually fall out. At that time, Yuki receives athletic advice and mental and physical support from her "coach", who has had feelings for Yuki that go beyond that of a teacher. But there are dark rumors about the coach...

(Source: Fanza, translated)

Note: It has a live-action AV adaptation: RKI-695 (2025/01/10)