Birthday: May 25

Height: 166 cm

Weight: 51 kg

Blood type: O

Status: Human

Koyomi is a resident of the same dormitory Michiru resides in. She is a very cheerful girl, but she also has a double personality. Unlike Koyomi's innocent and sweet exterior, her other personality, "Yomi", is without reserves and is usually fondling Michiru, despite the latter's unwillingness to do so. It appears that Michiru is the only person able to awaken this alter ego of Koyomi's, merely by kissing her or simply calling her by name.

While Yomi seems to dislike everyone other than Michiru (for whom Yomi harbours sexual desire and deeper emotional feelings), Koyomi seems to have a slight crush on Sotetsu Asō.

Yomi also has a special ability called the "Dead Man's Tongue", which allows her to channel dead people's words.