A Demon's Underling

A world where demons coexist with humans. While there have been no conflicts in the past between demons and humans, demons possess tremendous abilities, can use a variety of magic, and have the power to control humans as underlings. Demons are at the top of the biological hierarchy, so to speak. So now I, Toma, am the underling to the demon, Chiaki. Every night I have to feed him my bodily fluids to "replenish his magical powers". He licks me all over... Our lewd acts should have no meaning; our relationship is a master-servant one. But why does my heart ache so much...?