Marie attends the same jungle school as Haré and Guu. She is the younger sister of the school's perpetually sleepy teacher, Reiji-sensei (Lazy-sensei). Orphaned shortly after birth, Marie was raised alongside Haré by Weda and her brother Reiji until age four. This upbringing created a deep, almost familial bond with Weda, whom she greatly admires despite Weda's flaws, partly due to never knowing her own mother. She similarly views the school physician, Dr. Clive, as a paternal figure within her imagined family structure.

Marie exhibits a friendly and initially supportive demeanor toward Haré, which evolves into an intense romantic crush. Her feelings manifest as aggressive jealousy, particularly when Haré travels to the city; she frequently imagines him engaging romantically with various women in elaborate, self-pitying fantasies framed through a tragic, shōjo manga-esque lens. This jealousy drives much of her focus regarding Haré.

She possesses a creative passion for designing and sewing clothes, crafting outfits for herself and others. This includes creating animal-themed costumes for Dr. Clive, which he wears to encourage her. She also prepares meals for Clive, showcasing a nurturing aspect.

Her background and personality remain consistent. Six years after the primary events, she marries Haré, now a teacher at the village school. She later gives birth to their daughter. Upon seeing the newborn's distinctive smirk—identical to Guu's—Haré names the child "Guu," implying a connection to the enigmatic being who had erased herself from most memories. The baby subsequently displays Guu's trademark snarky attitude and demeaning behavior toward Haré.