In the anime 18if, Haruto Tsukishiro awakens in a strange bedroom inside a dream world and spots an unusual application on his phone. When he activates it, a mysterious woman emerges and attempts to drag Haruto into her domain, but a white-haired girl suddenly appears, saves him, and labels the woman a witch before the encounter abruptly ends. After Haruto returns to the dream realm, he encounters Katsumi Kanzaki, a talking anthropomorphic cat, and the white-haired girl assists them in escaping the witch’s minions through a portal.
Katsumi, who is well-versed in the dream world, explains that the girl—named "Lily"—frequently shows up across various dreamscapes. To leave the dream world, they must find a blue door. Upon reentering the witch’s territory, Lily reveals that witches suffer from "Sleeping Beauty Syndrome," a coma-like state caused by real-world trauma, and must be defeated in the dream world to wake up. After overcoming the witch and locating the blue door, Haruto and Katsumi say goodbye, promising to meet in reality. However, Haruto wakes up again in the dream bedroom. Driven to uncover the truth, Haruto and Katsumi explore the deeper mysteries surrounding the witches, Lily, and Haruto’s repeated confinement in this dream world.