Nidome Ha Shoujiki summary:

During one of his visits to a gay bar, Yamato, a refined top with a princely aura, chanced upon a porn video featuring Jin, a top with a wild character. After hearing rave reviews about the man's wondrous sex, Yamato's curiosity piques as a fellow top. Promptly, he goes to visit Jin and seeks out the man's expertise. But Jin's condition is to teach through practice, and that's where our story begins!