I'm Banging My Rival From A Parallel World!?

Summary

Amatatsu is a brash, but normal high school student until he wakes up in the middle of doing it with another guy!! To make matters worse, the culprit is his biggest rival, Sen! Is it really possible he's come to a parallel world where he and Sen are a couple...!? In addition to the main story, there are other complicated love stories about a guy with a voice fetish, a boy with a crush on his best friend, and a chubby chaser.