Read Yuri Love Slave: Futari dake no Houkago Manga:
Asakura is an ordinary high school girl. Once upon a time, she accidentally saw Reina, the class president who was rude and stiff, going to a bookstore. Asakura followed the chairman, and discovered that book the chairman bought turn was a gay manga.
Asakura, who was surprised by it, along with a feeling of shame, opened and read contents of the book, and over time something tic more.. kled her crotch. The devil's grandson whispered - "Dear Asakura, don't you want to try the things in this book? Don't you want to feel kimochii?"
Ignoring the angel's warning on her right shoulder, Asakura's plunged into the devil's seduction, and her gay adventure with Reina begins...