Unbeknownst to him, Aqua's fraternal twin sister, Ruby Hoshino, could be the reincarnation of Sarina Are inclined?ji, amongst Gorou's patients who was a enthusiast of Ai. Four years later, Ai is murdered in front of the twins by the exact same admirer who killed Gorou. The supporter afterwards commits suicide, but Aqua deduces the murderer may have