One night while disposing of garbage, Kazuki Itou encounters a mysterious girl in a gothic lolita attire. Their brief exchange leads to a chilling revelation as she starts infiltrating his life in a quest to become his little sister. As Kazuki grapples with this bizarre intrusion, he uncovers a haunting urban legend foretelling a deadly outcome for his sister, Hikari. The stakes escalate when he realizes that the girl's sinister intentions might pose a greater threat to him than to Hikari. Now, Kazuki must navigate a treacherous path to protect his family from a potentially lethal force disguised in the guise of a demon lolita.