Sodachi Oikura is a third-year student at Naoetsu Private High School and a childhood acquaintance of Koyomi Araragi. Her childhood was marked by significant trauma stemming from an abusive home life, leading her parents to place her temporarily under the protection of Araragi's family, both police officers. Witnessing the Araragi family's happiness intensified her awareness of her own family's dysfunction, fostering deep resentment and alienation. Reconnecting with Araragi as his junior high math tutor, she hoped he might recognize her plight and intervene. His failure to recall their earlier connection or perceive her suffering deepened her bitterness. In their first year of high school, she organized a math study group before final exams. When test results showed irregularities between attendees and non-attendees, she initiated a class trial to identify a potential leak. The proceedings devolved into chaos, culminating in a majority vote falsely implicating her as the culprit, manipulated by the teacher. Araragi's inability to steer the trial or support her cemented her hatred. After a two-year absence, she returned to school harboring intense hostility. During a confrontation, she stabbed Araragi's hand with a pen and later engaged in a physical altercation with Hitagi Senjougahara, resulting in her being knocked unconscious. A visit to her government-subsidized apartment revealed her psychological instability and circumstances: her father imprisoned for domestic abuse, her mother abandoning the family and later dying in an accident – an event Sodachi blamed on herself. Her self-loathing manifested as a desire to cast Araragi as her "villain" to avoid confronting her trauma. Tsubasa Hanekawa, drawing from her own experiences with abuse, challenged Sodachi's resignation, urging her to seek happiness over despair. This marked a turning point, leading Sodachi to acknowledge her potential for change. In the *Zoku Owarimonogatari* Mirror World's alternate reality, trauma's absence reshapes Sodachi's life. Adopted by the Araragi family in elementary school, she develops a cheerful, affectionate demeanor, sharing a sibling-like bond with Koyomi, including a shared bedroom. She retains her love for mathematics, frequently solving puzzles with him. Despite apparent contentment, she expresses unease that her happiness feels "unreal," a sensitivity heightened by Koyomi's presence—his real-world memories subtly influence her, causing distress. Shinobu Oshino later confirms prolonged exposure risks destabilizing her psyche by revealing the paradoxes of her existence. Years later, as a 23-year-old municipal clerk, Sodachi reunites with Araragi. Their history includes a brief college reconciliation orchestrated by Hanekawa, during which she lived with the Araragi family. When this caused Senjougahara to break up with Araragi, Sodachi intervened to reconcile them, threatening suicide to compel their reunion. After the couple's second breakup, she severed ties entirely. Meeting at the town hall, she displays familiar bitterness, insulting him while agreeing to lunch. She reveals purchasing her derelict childhood home to renovate and "paint over" her traumatic memories, aspiring to build a new family there. She also proposes a pact: if both remain single by age 30, they will strangle each other. Her personality combines intellectual passion—particularly for mathematics, which she describes as "beautiful"—with deep-seated emotional volatility. Competitiveness earned her the nickname "How Much" (a pun on "Oikura"), which she resents. Unlike others who cope via supernatural oddities, she directs her blame squarely at Araragi, viewing him as the root of her misfortunes.