The older of the two twin maids in the Tohno mansion, Kohaku, along with Hisui, is a childhood friend of Shiki. She wears a Japanese kimono and is always seen to be smiling and cheerful, being especially gifted with medicine. Her name, Kohaku, is the Japanese word for amber, referring to her eye color. She hides her tragic past behind a cheerful face and Hisui's cold demeanor. Like Hisui, Kohaku is a Synchronizer, a person that can give someone life energy through exchange of body fluids.

Kohaku was a member of a branch family of the Fujou clan, but was brought with her sister Hisui to live in the Tohno mansion, because the Fujou clan had a special power of giving others energy. Makihisa Tohno needed this ability in order to keep control of his body.