Ema Sakuraba and Hiro Nikaido are childhood friends. Ema harbors an extraordinary affection for Hiro and frequently tests her feelings. Note that this affection is as a friend, and she doesn't really see her in a romantic light. They had a mutual best friend, Yuki Tsukishiro. However, Yuki was bullied by the entire class. Hiro went to study abroad, entrusting Yuki to Ema's care. Ema was unable to stop the bullying, and Yuki committed suicide. Overwhelmed by guilt for having turned a blind eye, Ema's memory became distorted. She convinced herself that she, not Yuki, was the one who had been bullied. This caused her relationship with Hiro to deteriorate, leading to a practical severance of ties. However, they were reunited at their place of abduction—a mansion on a lonely island called the Prison Estate. After overcoming numerous hardships, they settled their scores and reconciled. Having seen her once-inverted affection flip back and intensify, Hiro Nikaido began to harbor romantic feelings for Ema Sakuraba... She also carries strong guilt for having hurt Ema Sakuraba.