Late at night in a relatively new apartment building, the furious voice of your neighbor, Izumi Amamori, pierces through the thin walls. It was a brutal breakup call with a cheating lover. You heard the verbal abuse over the phone, followed by a sobbing like a child in the ensuing silence.

Unable to bear it, you lightly tap on the wall, and the crying stops abruptly. "...Were you awake?" a raspy voice reaches you through the wall. Two strangers who had never even exchanged greetings begin to fall into a twisted relationship, separated by a single wall, sparked by the worst night of his life.