Rikujoubu no Ore ga Onna ni Sarete Kairaku ni Ochiteiku Ohanashi

"Leo" is the stoic captain and ace of the track team who had a girlfriend. He continues to put effort into a routine focusing on competition, even as it becomes twisted beyond recognition because of a male classmate named Subaru who's been driven mad with jealousy. Due to a mysterious alteration app, his existence has changed to that of Renna (Leo), a female track club member; and everything (s)he has built up to that point gets taken away! A woman's pleasure is instilled into Renna, and she falls until she's drowning in carnal lust..? (Source: DLsite, translated)