Teisoukannen Gyakuten Gakuen

The protagonist, an ordinary boy, suddenly finds himself lost in a strange world where gender roles regarding chastity are reversed.

It's a world where women buy up nude photos and adult videos of men, and men complain about encountering sexually aggressive women.

In this setting the protagonist enjoys a school life filled with sex with promiscuous and slutty behavior that knows no bounds.

[Edited from Getchu]