Yoru is plagued by vivid, erotic dreams involving strangers, only to discover that her sister, Asahi, leads a double life as a sex demon exterminator. By diving into the "Deep Stratum," a collective dream realm, the sisters hunt demons that possess humans through their subconscious. After realizing she possesses rare supernatural abilities within this realm, Yoru transforms into the warrior Night Tail to join her sister's crusade.
After battling a sex demon in a client's dream, Yoru experiences strange, erotic visions before teaming up with Kouhei to search for her missing sister and Shirou. Their investigation leads them to a mysterious warehouse where they encounter a girl named Menou, whom Kouhei recognizes from his own dreams, suggesting a deeper mystery behind the Good Night Club.