Ban ni Natte, Goshujin-sama

This is a world where humans keep beasts and beasts obey humans. Born as the second son of a well-known family, the lonely Reiji has always had his beastman servant, Tsubaki, as an irreplaceable presence since he was a child.

But one day his feelings turn to love, and Reiji playfully kisses Tsubaki, which invites his bestial lust. His sharp bite overflows with his own repressed feelings, but comes with a dark realization — they are different races, different castes. Can they overcome these hurdles and embrace their love?

(Source: TOKYOPOP)

Note: Chapter count includes two extras.