Ruka's older twin sister. Rumi is a little more tomboyish than Ruka. Rumi and Ruka both loved Katsuyuki, but Katsuyuki fell in love with Ruka. Since her envy and hatred for Ruka have been increased by the virus, she turns evil. When she gets the supernatural powers as Ruka, Rumi gets the ability to control a person with the virus, using her saliva and blood to infect them. Rumi commits atrocities to force Katsuyuki to be with her.