Emma Sakuraba and Hiro Nikaido are childhood friends. Emma harbors an extraordinary affection for Hiro and often tests her feelings. However, this affection is strictly as a friend, and she doesn't see her in a romantic light. They shared a mutual best friend, Yuki Tsukishiro. However, Yuki was bullied by the entire class. Hiro went to study abroad, entrusting Yuki's well-being to Emma. Emma failed to stop the bullying, and Yuki committed suicide. Overwhelmed by guilt for being a bystander, Emma falsified her own memories, convincing herself that she was the one being bullied instead of Yuki. This led to a breakdown in her relationship with Hiro, resulting in a total estrangement. However, they were reunited at a mansion on a remote island called the Prison Mansion. After overcoming numerous hardships, they settled their scores and reconciled. Hiro's feelings, which had once inverted into hostility, flipped back and intensified into romantic love for Emma. Hiro also carries a strong sense of guilt for having hurt Emma in the past.