Rin Usuda is a troubled young man. He has a problem with his ass. Or rather, the funky birthmark on his ass. Obviously he's not been able to hold a normal relationship with any girls.

Another problem is that Rin has a massive crush on Chizuru Izumiya. He even frequents the hospital she is working in, if only to have late night coffee.

However, one day, Rin discovers that his ass has magical powers. Sexy magical powers...