Challengers(1996)

Genius-level freshman Tomoe Tatsumi was smart enough to get accepted into a private college in Tokyo, but too naive to realize there wouldn't be enough money left over for rent. So, how is it that he's living in a fabulous apartment for less than most people pay for a single room?

It is thanks to white-collar worker Mitsugu Kurokawa, a good Samaritan with an ulterior motive: to love, honor, and cherish this irresistibly charming student until his dying days! ...Which may come sooner than not if Tomoe's violently homophobic older brother Souichi has any say in the matter.

(Source: DramaQueen)