Mount Position! summary:

Ichito, a high school teacher, is supposed to be living together with his lover... but he walks in on his boyfriend having an affair! Suddenly, the mysterious man who helped him to his apartment is furious. In fact, the man is Ryugasaki, the other guy's boyfriend! The stunned Ichito is pushed down by Ryugasaki who says he must "take responsibility" and then he takes his virginity!!