Shizuki is the older sister of the "Akuma Twins". Being the older, she is sarcastic, lazy, and smart, but she has a weak body; she can get sick and tired easily, cannot swim in pools as a result of the chlorine, and almost was killed by Tatsuya's food. She has an immortal body and has lived for centuries. She gave immortal bodies to Seine and Shimon. Her former name was "Pistis Sophia" but she changed because it was "stupid". She is a Oyaji-con (she is attracted to "handsome" grown up men). The name Pistis Sophia is a character from an earlier work of Yuna Kagesaki's: Chibi Vampire, who is actually their younger sister Psyche. Shizuki and her sister call Seine "Sehne".