Ai has had a crush forever on her classmate Tatoe. When she finds out that Tatoe is in a secret relationship with another girl, she sets out to sabotage their plans for the future.

While celebrating with her friends in her new cheaply rented apartment on the thirteenth floor of a building, the young Sayaka unexpectedly jumps off the balcony committing suicide. Her mother goes insane and her older sister, Mariko, decides to investigate the mysterious death of her sister.