The younger of the two twin maids in the Tohno household, who wears a Western-style maid uniform and takes care of Shiki when he returns home. Her name, "Hisui," means "jade" in Japanese, reflecting her green eyes.
She acts cold and unfeeling, but it is only an act to hide her kinder nature for the sake of her sister. She is a Synchronizer, a person that can give someone life energy through the exchange of body fluids.