 If you liked
Makai Ouji: Devils and Realist
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 ...then you might like
Bloody†Mary
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borderline bl with identical premise: a demon/vampire appears in this boy's life and demands a certain something from him. because the two are connected by some sort of fate, the boy is now the target of other demons or vampires. while he feels repulsed with the idea of getting along with his demonic buddy, he has no choice but to accept his protection.