Rumi's twin younger sister. Ruka is shyer than Rumi. however, sometimes, she becomes emotional like Rumi. Ruka was infected with a virus at an old burial mound, and she gets supernatural powers (flying in the sky and power pass-through), and an antibody to virus which Rumi scatters. Ruka falls in love with Touma Katsuyuki. She is in a dilemma because of her love for Katsuyuki and her love for Rumi. Ruka confronts Rumi with Katsuyuki. However, she hopes that she will be reconciled with Rumi.