From Renta!:

Worried about his unattractiveness to women, Koichi secretly buys an adult toy to train up his masculinity. But, his plan gets discovered by a man living in his apartment block, Shu, who happens to work in the adult film industry! Right when Koichi thinks he's about to be blackmailed, Shu makes a surprising proposal: He offers to help Koichi draw out his inner manly man and find out what true pleasure feels like! When Koichi starts taking lessons in bedroom intimacy, he finds that Shu's sweet, provocative caresses stir pleasures in him he'd never known...