The constant companion in Yuu's existence has been her identical twin, which means she has a "copy" of herself at her side. With the latest scientific advancements, a more refined replica has been created, and Yuu is the perfect subject to experiment on. Nevertheless, as her clone grows more intelligent and starts to question its own existence, the experiment runs the risk of becoming overwhelming. The distinction between authentic and replicated begins to fade away, prompting everyone to ponder whether a "copy" that has exceeded its origin is only a copy, the source itself, or something completely new.
