Rem Ayanokōji descends from Dream Guardians, psychic warriors who enter human dreams to battle life-draining nightmare demons. Her age appears ambiguous, often resembling a junior high student, and she withholds details about her family or past. She runs Tokyo's Ayanokōji Detective Agency, tackling supernatural phenomena through word-of-mouth cases—primarily investigating dream invasions and demonic threats.

Her companions include Alpha, a kitten shifting into a battle-ready wild cat, and Beta, a spirit-tracking puppy that grows into a combat canine. Allies feature Enkō, a martial arts monk harboring romantic feelings for her, and Umimaru Kidō, a rival psychology professor and tech expert. Detective Junichirō Sakaki joined her network after she resolved a nightmare case involving his daughter Yukari. Antagonists include Dr. Shinigami—later exposed as Shimura, a fellow Dream Guardian descendant using his powers for murder.

Across OVAs like *Dream Hunter Rem* and *New Dream Hunter Rem*, she confronts entities such as a demon at Seibishinjo Academy, a headless knight tied to her 12th-century ancestor, and Dr. Shinigami’s dream-based killings. In *Massacre in the Phantasmic Labyrinth*, she battles Dr. Frankenstein and android Julian within a dream labyrinth. Her dream form wields swords, while real-world conflicts employ a Colt .44 Magnum and a missile-equipped car. She intermittently interrupts stories to explain dream science.

Manga spin-offs like *Dream Hunter Rem XX* depict her fighting tentacle entities on a galactic dream train, while *Dream Hunter Rem Alternative* introduces fellow hunter Kanon Takatori. She appears as a playable character in *Super Heroine Chronicle*. Her narratives consistently weave supernatural horror, action, and mystery, exploring beauty, trauma, and the repercussions of dreams invading reality.