A beautiful young girl, Rio Sakamoto, wanders the streets searching for her friends who are disappearing one after another. Exhausted and at a dead end in her search, Rio receives a call from one of her missing friends... Unaware it's a trap, Rio summons her courage to rescue her friend and ventures alone into the Black Lion Society's office... There, she is forced to drink a powerful aphrodisiac and loses consciousness! When Rio wakes up, what awaits her is...