Rumi's younger twin sister. Ruka is shyer than Rumi. However, sometimes she becomes just as emotional as Rumi. Ruka was infected with a virus at an old burial mound, and she gets supernatural powers (flying in the sky and the power to pass through objects), and an antibody to the virus which Rumi scatters. Ruka falls in love with Touma Katsuyuki, finding herself torn between her love for him, and her love for Rumi - who loves Katsuyuki too, and is violently possessive of him. However, she hopes that she can reconcile with Rumi.