Yakyuubu no Moto Ace ♂ wa Sei Shori Pet ♀

A jealous teammate uses a magical hypnosis smartphone app to turn the male MC into a sex-addicted girl both mentally and physically, then has the now female MC use the same app to erase the memories of everyone that remembered she was originally a boy. Why? So the teammate could NTR the MC's girlfriend in front of him/her, which only makes the MC jealous of her ex-GF.

Yaoi tag added due to a few scenes of the male MC having sex with other men while under the influence of the app.