Sodachi is first presented as an intense and confrontational individual, but in her earlier years, she displayed a much gentler and kind-hearted personality. The younger Sodachi that Koyomi Araragi once knew was more composed and emotionally open.

As a high school student, she is often described as someone who observes others critically, as though constantly evaluating them. Sodachi possesses a strong sense of competitiveness, which contributes to her reputation among her peers resulting in an unflattering nickname she deeply resents. She has a deep admiration for mathematics, often describing the subject as beautiful. Her antagonism toward Koyomi is particularly fierce, largely due to his academic performance in math, which she interprets as an affront. This hostility manifests in a harsh and obsessive hatred, driven by unresolved emotions and a troubled past.

Sodachi is a pale-skinned girl with long silver-gray hair and gray eyes. She typically wears the standard Naoetsu Private High School uniform, similar to that of Tsubasa Hanekawa and Hitagi Senjougahara. Her hair is styled into twintails, adding to her sharp and distinct presence.

In Zoku Owarimonogatari, her Mirror World counterpart is portrayed with shorter hair and a noticeably more cheerful and approachable personality, contrasting sharply with her usual somber and intense appearance in the main timeline.

Sodachi served as the class president during her first year of high school, in a class that included both Koyomi Araragi and Hitagi Senjougahara. At the time, she requested to be called “Euler” as a tribute to the mathematician, reflecting her passion for mathematics. However, her classmates gave her the nickname “How Much,” a pun on her surname (Oikura, which sounds like “how much” in Japanese) and a jab at her critical attitude.

Two years prior to the main events of the series, Sodachi organized a study group ahead of the final exams. She scored 99 out of 100 on the mathematics test, ranking second in the class. However, a noticeable disparity in the results between those who participated in the group and those who did not led to suspicion that someone had leaked the exam questions. In response, Sodachi convened a class meeting to identify the responsible party. Although the discussion was inconclusive, the majority of the class ultimately accused her of being the culprit, resulting in her social ostracization.

Despite the accusation, Sodachi continued to study on her own but remained absent from school for the following two years.

Unbeknownst to him at first, Koyomi had encountered Sodachi earlier in life when his parents, both police officers, offered her shelter in their home due to troubles in her own household. During this time, she also became acquainted with Karen and Tsukihi Araragi, as well as Nadeko Sengoku, who frequently visited the Araragi household.

Koyomi Araragi
Sodachi shares a complicated and emotionally charged history with Koyomi. Although they were childhood acquaintances and once attended the same study group, their relationship is strained by misunderstandings and unresolved trauma. Sodachi harbors deep resentment toward Koyomi, stemming from both personal and academic frustrations. Despite her hostility, their past is deeply intertwined, and Koyomi plays a central role in confronting the events that shaped her present self.

Hitagi Senjougahara
As classmates in their first year of high school, Sodachi and Hitagi have minimal direct interaction, though they share a mutual connection through Koyomi. Hitagi’s calm confidence often contrasts sharply with Sodachi’s intensity, highlighting the differences in how each copes with emotional pain and isolation.

Karen and Tsukihi Araragi
Sodachi briefly lived with the Araragi family during her childhood, which allowed her to become familiar with Koyomi’s sisters. While their relationship was limited, the time spent in the household left a lasting, if unspoken, mark on her memories.

Nadeko Sengoku
During her time living with the Araragi family, Sodachi also met Nadeko, who frequently visited the house. Their interactions are not deeply explored, but they represent another piece of Sodachi’s forgotten or suppressed past.