There have been multiple strange cases where people have been losing parts of their bodies after opening an email with the subject "Down". Kanno, a software programmer working for the Cyberphone company, is suspected as the owner of the cellphone that sent the emails.

A lover who commited suicide six years ago, a homemade AI program, and a strange series of emails... what will Kanno discover in the overlapping strange spirals of this mysterious serial case?