Vampire-Sama No Mazui Gochiso summary:

"Without further ado, I shall receive your blood.” At a vampire auction where human blood is sold, Nicholas, blood rank D, is unexpectedly purchased by the elite vampire Xenon for 10 million yen. Initially, Xenon seems arrogant, but as Nicholas sees his unexpected side, he starts to open up to him. Meanwhile, Nicholas becomes concerned about only receiving blood transfusions and not being directly sucked by blood. Will this lead to something more? A "vampire contract love" brought to you by the ultimate tag team of Aiba Moko and Sakai Yukari!