Mayoi is cheerful, energetic, and inquisitive, fitting her youthful appearance. She frequently makes spelling mistakes and has a habit of deliberately mispronouncing Koyomi Araragi’s family name, a playful quirk she eventually admits to doing on purpose. Although she is generally friendly, Mayoi remains cautious around strangers and is quick to defend herself if others become overly intrusive. This guarded behavior is later revealed to be intentional, aimed at discouraging people from following her and becoming lost.

Despite her playful nature, Mayoi displays a timid side around individuals she finds intimidating, such as Hitagi Senjougahara, who openly expresses her dislike for younger girls. However, after ascending to godhood, Mayoi overcomes much of her former timidity. She becomes confident enough to engage with powerful beings, such as Deathtopia Virtuoso Suicidemaster, a vampire prepared to kill her, who was surprised by her fearless attitude.

Although she appears to be an 11-year-old girl, Mayoi often exhibits unexpected maturity, particularly when offering advice or listening to Koyomi’s personal struggles. Her ability to handle complex emotional issues highlights a depth beyond her apparent age.

Mayoi is a young girl with long black hair styled into pigtails and dark red eyes. She wears a white headband decorated with a white swirl on each side. Her outfit resembles a typical elementary school uniform, consisting of a white blouse connected to a dark blue skirt by two straps, complemented by white socks and pink shoes.

A notable feature of Mayoi’s appearance is the large pink backpack she always carries, shaped like a large chick. The backpack contains various items, including a large paw and several small plush dolls. Koyomi Araragi once remarked that without her backpack, Mayoi looks drastically different, comparing the change to “a snail turning into a slug.”

Later in the series, after ascending to godhood, Mayoi assumes the form of a young adult woman dressed in a shrine maiden outfit, appearing around the same age as Koyomi.

Mayoi grew up in a broken family following her parents’ divorce at an early age. Custody was granted to her father, and over time, Mayoi’s memories of her mother began to fade. Longing to reconnect, she set out alone to find her mother’s house. Tragically, during her search, Mayoi was struck and killed by a truck on May 14, the day before Mother’s Day.

After her death, Mayoi became a wandering spirit, continuing her quest to locate her mother’s home. For the next decade, she roamed alone, intentionally pushing away those who tried to help her in order to prevent them from becoming lost under her influence. Despite her largely solitary existence, she occasionally indulged in playful mischief, intentionally leading school children astray for amusement.

At one point in the series, Koyomi Araragi teases Mayoi by playfully altering her surname, calling her “Hachihachiji,” “Hachishichiji,” and “Hachirokuji.” In each variation, he replaces the “ku” (九, meaning “nine”) in “Hachikuji” with other numbers—”hachi” (八, eight), “shichi” (七, seven), and “roku” (六, six) effectively diminishing her name with each substitution. Mayoi protests that he is “taking temples away” from her name, a playful reference to the original meaning.

Mayoi’s surname, 八九寺, literally translates to “89 temples.” The “temple” reference stems from the character 寺 (ji), which means “temple.” Additionally, the kanji for “eight” (八) and “nine” (九) can be read together as “yaku,” which means “misfortune” (厄) in Japanese. This reading ties into a Buddhist trope where pilgrimages traditionally involve visiting 88 temples, and being the “89th temple” symbolizes misfortune or being out of place.

Mayoi’s given name (真宵) can be interpreted in several ways. The standard reading conveys the meanings “true” (真) and “evening” (宵). Alternatively, it can be associated with the word 迷い (mayoi), which means “to lose one’s way”—a fitting interpretation given her fate as a wandering spirit.