A woman plummets from the roof of a building. But who she is and whether she jumped, fell, or was pushed remains unknown, as the body was too mangled by the impact to make out her features, and she carried no form of identification. The sole clue to her identity is her cell phone which contains only two numbers: a woman claiming to be her twin, yet who has no official documentation; and the popular author Shun Mizorogi, who remains secretive about his relationship with the deceased...