Black Black Lotus

Renna, just transferred to Fuyou Girls School, meets Kyouko, who is called "Black Rose" and respected by everyone. Black Rose is beautiful, mysterious, and seems to know Renna. She tells that it's Renna's voice that attracts her, and that was why she saved Renna when they were in grade school. Suddenly Renna remembers...the reason why she had to change school and move to a remote place four years ago. It was something she forgot to protect herself. Renna is devastated when she knows that Black Rose is dead...she was supposed to see her on the day she was killed! When Renna receives a black card that invites her to "Black Black Lotus", a murder matching website, she finds out that someone who used her name killed Black Rose. Who is that!?