Bara wo Karasu Te de Boku wo dake

Makoto Hourai is given to Alice Kamiya as an "offering" because of a long-established contract between the two families. He is there in order to assist Alice, who is actually a vampire. As an offering, Makoto is supposed to give Alice his blood, however, he is anemic. How does Alice manage to drink blood, if Makoto can't provide for her? How does Makoto feel about all this?

(Source: Intercross)