Rikou Takitsubo is a high school-aged esper and core member of Academy City's mercenary group Item, operating within its dark side. Her perpetually lethargic appearance features tired-looking eyes and evenly cut shoulder-length black hair, often paired with a practical pink tracksuit worn as casual attire and sleepwear, reflecting her functionality-over-aesthetics approach. Subdued and emotionally reserved, she displays deep care for close companions despite an airheaded reputation from blank stares and sleeping with open eyes, rarely voicing inner thoughts. Involved in criminal activities yet fundamentally kind and valorous, she demonstrates loyalty through actions like rooting for Frenda during missions or volunteering as bait to protect allies regardless of personal risk. Her relationship with Hamazura Shiage becomes central after he shields her from Mugino Shizuri's vengeance; she falls in love with him, later showing possessiveness toward rivals like Fremea Seivelun. Their dynamic evolves into a familial unit resembling married parents caring for a child. Circumstantial evidence suggests she may have been a "Child Error" (Academy City orphan). Falsely arrested in a researcher-orchestrated scheme to acquire her for experimentation, she was freed by Mugino Shizuri’s intervention, becoming Mugino’s longest-serving Item recruit. Researchers secretly manipulated her Item induction and Ability Body Crystal usage to unlock her latent potential. Her Level 4 esper ability, AIM Stalker, detects, memorizes, and tracks unique AIM diffusion fields across vast distances, providing precise directional data. Initial activation required the Ability Body Crystal drug, causing severe physical deterioration with repeated use. Healed by Elizalina Alliance intervention during World War III, she shed her drug dependency and later expanded her power to sense magical energies like those from Orsola Aquinas or Golden Dawn members, drawing warnings from entities like Niang-Niang about her "connective type" nature. Researchers, including Kiharas, theorized her potential as the 8th Level 5 esper: fully realized AIM Stalker could manipulate Personal Realities and AIM fields to elevate/suppress esper levels, grant/remove abilities, swap powers, or create Dual Skill phenomena—rendering Academy City’s Power Curriculum Program obsolete. Tree Diagram simulations deemed this outcome "too severe," leading to flawed drug experiments. Figures like Mugino and Kakine Teitoku acknowledged her power-disrupting capacity; Kakine speculated she subconsciously influenced his Dark Matter. Her experiences with Shiage catalyzed this progression. Her chronological development begins in the "Battle Royale Arc," aiding Item against rivals like SCHOOL. Overhearing Shiage despair over Level 0 expendability while disposing of a body deepens her concern for him. After Mugino executes Frenda for betrayal and targets Rikou and Shiage, they flee together. During World War III, they reach the Elizalina Alliance for her curative treatment. Post-reconciliation with Mugino, Item reforms, remaining active after the October 9th factional war. Later actions include stabilizing Mugino’s Meltdowner ability and participating in conflicts like the search for Fremea.