Umi no Yami, Tsuki no Kage

Ruka and Rumi Kobayakawa are twin sisters in love with the same man, athletic upperclassman Katsuyuki Touma. At first Rumi is supportive of Ruka's fledgling romance with the handsome Katsuyuki, until the twins are infected with a strange bacterium that alters Rumi's personality and gifts the twins with terrifying psychic powers. Now Rumi will let nothing - or no one - get between her and Katsuyuki, including her own twin sister.