Doukyonin ga Ore de Yoisugiru Hanashi

"My roommate is a vampire who gets crazy when drunk." Hiyori, a high school boy who lost his parents when he was young and has no relatives, puts up a vacant room for rent in order to earn some income. A mysterious man, Yoki, came to him. He is a vampire who wants my blood! Moreover, when he drinks my blood, he gets drunk and becomes a bit of a drunkard, demanding more. In such a dangerous life together, one day Yoki told me that we had a contract as a mate since we were young..?