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Shadow breather - Deprives from sun breathing/flame breathing OR Moon breathing!
Needs a certain amount of light to create shadows!
An incredibly anxious person who can't stand socializing, because of his dismissive attitude towards others in the hopes of avoiding chitchat he comes off as cold, rude and stern, being misunderstood, not that he necessarily cares or minds, he'd rather they think badly of him if they are to leave him alone than the opposite.
Pretty efficient at demon-slaying and he likes to behead them before they have the chance to talk to him, man doesn't wanna get stuck in their monologuing and have the possibility of having a conversation.

Is a Marechi, due to many people dying to protect him because of his blood type, including family, he decided that instead of staying in normal civilization, running and getting others killed, he'd become a demon slayer so he could protect himself against those who'd want to consume him.