Rikō Takitsubo operates as a core member of Academy City's dark side mercenary group, Item. She possesses shoulder-length black hair and consistently wears a tired expression, favoring practical clothing exemplified by her frequent use of a pink tracksuit for both casual wear and sleepwear, prioritizing functionality over aesthetics. Personality-wise, Takitsubo maintains a predominantly lethargic, stoic demeanor, often appearing blank or spaced out while rarely voicing her inner thoughts. Despite this subdued exterior and her dark side involvement, she exhibits a fundamentally kind, selfless nature. She demonstrates care for her teammates, roots for them during missions, and willingly places herself in danger to protect others. She harbors strong possessiveness and deep affection for Hamazura Shiage, later developing a dynamic resembling a marital relationship with him, including a protective, albeit impatient, attitude toward Fremea Seivelun. Her background suggests she was likely a Child Error, with Item representing the only place she felt she belonged. Framed for a crime she did not commit, leading to her arrest—potentially orchestrated by researchers seeking access—she was freed and recruited into Item by Mugino Shizuri's intervention. Takitsubo had been with Mugino the longest among the group's members. Unbeknownst to them, her recruitment and subsequent provision of the drug Ability Body Crystal were part of ongoing Academy City research experiments probing her potential. Takitsubo's esper ability is AIM Stalker, classified as Level 4. This power enables her to detect, memorize, and track the unique AIM diffusion fields emitted by other espers, allowing her to locate targets through obstacles or across vast distances. Initially, she required Ability Body Crystal to activate her power. Prolonged use severely damaged her body, causing collapse, serious illness, and risking fatality. Healed by Elizalina in the Elizalina Alliance of Independent Nations during World War III, she could subsequently use her ability without drugs and unexpectedly demonstrated a capacity to sense magical presences, which induced sickness. Academy City identified her potential to become the 8th Level 5 esper. At full potential, her ability could manipulate others' Personal Realities, enabling her to increase or decrease esper levels, grant or remove abilities, switch powers between individuals, and achieve previously impossible phenomena like Dual Skill. This potential threatened to make the Power Curriculum Program obsolete, positioning her as a singular "Academy Individual." Realizing this potential proved difficult, but experiences with Shiage and subsequent struggles opened the path toward achieving it. During conflicts, she learned to stabilize Mugino's Meltdowner ability and was theorized to have subconsciously influenced Kakine Teitoku's Dark Matter. Within Item, her primary role involves providing tracking and tactical support during missions using AIM Stalker, often operating behind the frontline fighters. She identifies threats, security layouts, and target locations for the team, proving particularly crucial for preventing Mugino from overexerting or causing collateral damage. Her ability makes her indispensable for locating targets and navigating complex environments. Her character development centers on her relationship with Hamazura Shiage. A pivotal moment occurred when Shiage expressed despair over the disposal of a nameless corpse, lamenting the cheap value placed on Level 0 lives. This deeply affected Takitsubo, fostering concern for his well-being and marking a shift toward valuing individual life despite her dark side involvement. Following Frenda Seivelun's execution by Mugino for betrayal, Takitsubo became estranged from Item and fled with Shiage. They struggled against Academy City's dark side together, eventually falling in love. After World War III, reconciliation occurred with the remaining Item members, and the group reformed. Takitsubo features across multiple official media. She is a main character in the "Toaru Anbu no Item" light novel series, detailing Item's missions and formation. This light novel received a manga adaptation serialized in Dengeki Daioh. An anime adaptation of "Toaru Anbu no Item" was announced on February 16, 2025, where she is a central character. Her story is integral to key arcs within the main "Toaru Majutsu no Index" light novels and related anime, particularly those focusing on Academy City's dark side and Item's activities. A voice drama written by Kamachi Kazuma was included with physical copies of the first light novel volume.