From Renta!:

Yuu is a bandsman who, despite being in the music scene, can't handle women and has never gotten laid. One day, on the way home from a concert, he encounters a suspicious man named Keita Kawabata. Keita instantly takes a liking to Yuu and offers to sleep with him to show him how to overcome his inexperience. But, it doesn't end there. Before Yuu knows it, he finds himself on his back!?