Butoukai no Techou

Butoukai no Techou summary:

Masahiro, who is a duke, has been studying abroad since he was young to learn about Western culture. Now he is teaching ballroom dancing/ettiquette and keeps getting strange looks from one of his students, Fukaya. He notices his interest even more when he's looking at Masahiro's portrait on a dance card/booklet and decides to seduce him. And the drama, intrigue, and treachery ensues.