He's the only human in the Kirishiki househould. His job is taking care of the properties. Seishirou originally came from a distinguished family, but he found his parents vile and disgusting. Chizuru killed them both, but refused when Seishirou asked her to turn him into a vampire too, pointing out that since his parents didn't rise, he probably couldn't either. Since then, Seishirou has been with the Kirishiki family and thinks of them as his own, and occasionally gives blood to Chizuru.