Umi no Yami, Tsuki no Kage

Identical twins Lumi and Luka Kobayakawa are both on the track team and share a crush on the older student Katsuyuki Tohma, who ends up choosing Luka. Lumi feels betrayed by her sister, while Luka tries to avoid hurting her feelings. While heading to a graduation party for senior team members, they take refuge in a cave that is later revealed to be a mass grave. A strange odor from the cave causes the deaths of all present, with only the twins surviving. After the incident, Lumi undergoes a dramatic change in personality. One day, she appears in Luka’s room, seemingly emerging from the floor.