Matsuoka Renna, who has just transferred to Fuyou Girl's Academy, is reunited with Mayuzumi Kyouko, a friend from her elementary school days. Known as "Black Rose-sama" and the object of admiration among the students, Kyouko says that she had been worried about Renna ever since she moved out of town due to a certain incident. However, something is bothering Renna. In the midst of all that, it is announced that Black Rose is dead. As Renna is stunned by this news, she receives an invitation to a suicide-matching website known as "Black Black Lotus".