Momoe Sawaki is a 14-year-old driven to protect Wonder Eggs, hoping to resurrect her closest friend Haruka after Haruka's suicide. Profound guilt shapes her mission, stemming from her belief that rejecting Haruka's romantic feelings contributed to Haruka's death. This trauma deeply influences her actions and emotional state.

She possesses an androgynous appearance: tall, slim, with short auburn hair swept aside and dark green eyes. Her typical attire—a navy blue sweater over a white dress shirt, loose beige slacks, navy socks, and burgundy shoes—often leads others to mistake her for a boy, causing significant distress. Despite this presentation, she identifies as female, consciously using the masculine pronoun "boku" at times but switching to the feminine "watashi" when her gender is validated.

Momoe is kind, polite, and possesses a strong sense of justice, often prioritizing others' well-being. She demonstrates bravery and self-sacrifice, fiercely defending those she cares about, such as protecting her uncle Shuichiro Sawaki—Ai Ohto's teacher and later her mother's fiancé—from accusations of misconduct, sometimes straining her friendships. However, profound insecurity plagues her regarding her gender expression; reactions to being misgendered are visibly anguished. This sensitivity originates in childhood experiences of being perceived as male and unwanted romantic attention from girls drawn to her "masculine charm," which she interprets as deceptive, fearing she misleads others by not being recognized as female.

Within the dream world, Momoe operates primarily in a train station setting, battling manifestations of trauma called Wonder Killers to protect girls who died by suicide. She wields an umbrella modified with a spearhead. Later, she bonds with Panic, a miniature crocodile-like creature emerging from a jeweled necklace given to her. Her missions involve defending victims like Miwa, who faced sexual harassment and family blame, and Mizuki, who experienced societal pressures. Both girls confess romantic feelings toward Momoe, exacerbating her discomfort due to their initial perception of her as male; while Momoe does not outright reject Mizuki's advance, her reaction suggests ambivalence.

A significant shift occurs during an encounter with Kaoru Kurita, a transgender boy from a Wonder Egg. Kaoru explicitly acknowledges Momoe as a girl yet expresses romantic interest, sharing a kiss with her; unlike previous confessions, Momoe does not refuse his affection. Her sexuality remains ambiguous; she expresses attraction to boys, noting admiration for masculine features like Adam's apples, but also demonstrates openness to relationships with girls or boys, indicating her distress stems more from gender misidentification than orientation.

Her friendship with Ai Ohto, who immediately recognizes her as a girl, provides profound relief and validation, contrasting with Neiru Aonuma and Rika Kawai initially misgendering her. Flashbacks reveal evolution in her gender expression: after Haruka's death, she adopted more masculine clothing and began using "boku," despite identifying as female, whereas she wore a feminine school uniform during her friendship with Haruka, the only person who consistently affirmed her gender. The narrative implies Haruka's suicide may relate to Momoe's rejection or broader societal harassment.

Throughout her journey, Momoe's struggles with identity persist. She questions Panic about its gender, expressing unconditional acceptance—reflecting her own desire for validation. Participation in traditionally feminine activities, like wearing a green dress for a date or painting nails with friends, coexists with her everyday androgyny. However, a date ends poorly when her companion realizes she is not a boy, highlighting the ongoing conflict between her self-identity and others' perceptions. Aspects of her gender identity remain unresolved.