Rikou Takitsubo operates as a Level 4 esper within Academy City's dark side, initially a core member of the mercenary group Item. She possesses shoulder-length black hair and perpetually projects a tired expression. Her practical nature manifests in a consistent preference for functional clothing, notably a pink tracksuit worn as both casual wear and sleepwear—an outfit others recognize for its overflowing practicality. Takitsubo presents a lethargic, emotionally reserved personality, often appearing as an airhead who stares blankly or sleeps with her eyes open. Despite this subdued demeanor, she demonstrates underlying kindness and fierce loyalty toward teammates, openly rooting for them. Her actions within the dark side reveal an inherent humanity and valor. She exhibits selflessness, repeatedly offering herself as bait to protect allies regardless of personal risk. This contrasts with moments of intense possessiveness, particularly toward Hamazura Shiage, whom she later develops romantic feelings for. Impatience surfaces around disruptive individuals like Fremea Seivelun, sometimes manifesting as threats of violence requiring Shiage's intervention. Likely a former Child Error, researchers identified the exceptional potential of her AIM Stalker ability, theorizing it could elevate her to the 8th Level 5 esper. Tree Diagram simulations indicated achieving this required prohibitively severe conditions, leading researchers to experiment using Ability Body Crystal drugs—part of a project comparing her potential with Mugino Shizuri's. Falsely arrested on fabricated charges orchestrated by a lab seeking to acquire her, Mugino intervened to dismiss the charges and recruited her into Item, a move serving Academy City's covert research agenda unbeknownst to either. She remained Mugino's longest-serving teammate in Item. Her primary ability, AIM Stalker, enables precise tracking and detection of other espers' AIM diffusion fields. Initially requiring Ability Body Crystal for activation—causing her eyes to widen during use—prolonged dependency caused severe physical deterioration, risking fatal collapse. The core function involves recording and locating espers across vast distances, though claims of solar-system-wide tracking are likely hyperbolic. Her power evolved to sense magical energies, reacting to figures like Orsola Aquinas (fused with Isis-Demeter), Annie Horniman, Westcott, and Madame Horos. Magical entities such as Niang-Niang identified her as a "connective type" and warned her about channeling dangerous forces. Takitsubo's latent potential allows manipulation of AIM fields and Personal Realities, theoretically enabling control over esper abilities—strengthening, weakening, transferring, or removing them entirely. This could facilitate previously impossible phenomena like Dual Skill and render Academy City's Power Curriculum Program obsolete, effectively making her an "Academy Individual." Researchers believed realizing this potential would allow her to single-handedly replicate all Academy City's functions. Triggering this evolution proved difficult until experiences with Shiage provided the necessary emotional catalyst. Her chronological development begins during the Battle Royale arc assisting Item against School. Overhearing Shiage's despairing monologue about disposable Level 0 lives while disposing of a body, she internalizes his words and later shares them with Item, marking the start of her concern for him. Following Frenda Seivelun's execution by Mugino for perceived betrayal, Takitsubo flees with Shiage. Their relationship deepens into mutual protectiveness and eventual romance, with Shiage vowing to "bring happiness" to her. During World War III, her ability proves critical when she stabilizes Mugino's erratic Meltdowner power to save Shiage's life despite her own deteriorating health. After escaping to the Elizalina Alliance of Independent Nations, she receives healing from Elizalina, eliminating her drug dependency and allowing drug-free power use. Post-war reconciliation sees Mugino reforming Item with remaining members, making it the only dark side faction to survive the October 9th conflict intact. Takitsubo participates in later events, such as searching for Fremea without drugs. Her power's growth draws attention from figures like Kihara Yuiitsu, who notes her progress as "exceeding well." She joins Shiage during major conflicts, including Aleister Crowley's invasion of London, operating alongside central figures like Toma Kamijo and Accelerator. Subsequently, she and Shiage adopt a dynamic resembling a married couple caring for Fremea, though her demeanor lacks conventional sex appeal during mundane interactions like discussing detergent needs.