A young dhampir (half-human, half-vampire) who lived in the old mansion Kiyo inherited. As soon as he sees Kiyo he starts flirting with her and calling her his "bride". It is unknown at first if Kuroboshi really likes Kiyo for herself or for her sweet blood. Later though, he is very jealous if Kiyo is near any guy, and if anyone is being mean to her, he retaliates quite fast. He also likes to suck Kiyo's blood (although he does not succeed very often). As the series progresses, his feelings are declared to be serious. When Kiyo is unsure of how she feels about him, he becomes angry and doesn't talk to her till the play. Then, in front of the audience, while in the middle of a battle with Sou-kun, he wholeheartedly declares that with all his body and soul, he loves her.

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