Mayumi is a girl who lost her parents in a car accident; unable to deal with the overwhelming sadness, hatred and anger, she wishes only to be able to stop feeling altogether.

Five years later, the now 18-year-old Mayumi's sister is the first victim in a series of bizarre incidents that involve people receiving text messages indicating a certain body part, immediately after which said body part is removed - painlessly and without blood loss - from their body and disappears completely.

Initially, Mayumi's sister's ex-boyfriend, Kanno, is suspected for the crime because the texts were sent from his phone number. Mayumi, however, is reluctant to believe the man who was like an older brother to her is capable of such a heinous act, and vows to discover the truth behind this sudden crime wave, Kanno's ex-girlfriend who killed herself on Christmas Day five years ago, and the highly advanced A.I. that Kanno had been creating at the time: the designing of which has since ground to a halt.