Reizouko ni Negi ga Atta Kamo

Yota, a company employee who collapses from exhaustion on his way home from work, wakes up to find his ass being worked on by a stranger, Akito, a yakuza! After his co-worker, to whom Yuto is a guarantor, conveniently runs away, Akito is told he has to repay his 30 million yen debt...! Wanting to avoid working at a gay brothel by all means, they two figure out a different way for Yota to repay this debt. After a turn of events, Yota helps out Akito in a bind, and so begins a new bond complete with compulsory sex training and exploration.

(Source: MangaPlaza)