Gakeppuchino Darling Boy summary:

Kanata's the ex-number one host who's in a dry spell of unpopularity.The newest host to start working there, though, Iori, is currently number one and has been forcing Kanata to drink all of the drinks that clients order for him each and every day... Then one day, Kanata learns that Iori's been giving free advice to hosts who are worried about their sales stagnating. Kanata's willing to give anything a try as he goes and visits Iori's place, but Iori guesses that in order to understand the feelings of his female clientele, Kanata needs to bottom...!?This story features a junior dominating his superior with erotic techniques under the guise of lessons.