Vampire-sama no Mazui Gochisou

"Without further ado, I shall receive your blood." At an auction where human blood is sold to vampires, Nicholas, a blood rank D, is bought for 10 million yen by the elite vampire Zenon. At first, Zenon seems to be an arrogant person, but after seeing a surprising side to him, Nicholas begins to open up to him. However, he's constantly giving his blood through transfusions, and begins to worry that Zenon cannot feel the pleasure of drinking blood directly.

(Source: Hakusensha, translated)