Naisho no Yoshuu

A secret relationship that no one knows.

He started "secret practice" with his best friend's girlfriend. Kissing, holding hands… all of this was supposed to be preparation for doing it properly with his real girlfriend…!! Even though he knows this is wrong, his libido won't let him stop!! The naive and immature urges of adolescence are out of control…!! A unique of immoral romantic comedy that will make your heart pound!!

(Source: Nihonbungeisha, translated)