Maria Momosaka, known as Momo, is a prominent figure in the series. She possesses long silky hair, charming almond eyes, a refined appearance, and medium-sized breasts. Her initial demeanor projects care and sweetness, embodying the "perfect little sister" archetype from her acting past. Yet beneath this facade, she wields sharp manipulation skills and a capacity for menace when required. This duality originates in a troubled childhood within showbiz, shaped by her parents' influence, fostering a deep-seated hatred for most people whom she views as enemies, leading to profound loneliness. Only her sister Eri and later Sueharu Maru gained her genuine trust.

A child prodigy actor, Maria gained fame starring in the drama "The Ideal Little Sister." Early in her career, Sueharu Maru served as her mentor, helping her conquer personal fears. This guidance led her to idolize him, accepting him as a "big brother" figure and developing romantic feelings. When Sueharu abruptly abandoned acting, she lost contact. Years later, seeing his video from the Confession Festival, she sought him out at his school, confessed her love, and aimed to reconnect, intending to bring him back to the entertainment industry so they could achieve stardom as a couple.

Her family history involves abusive parents whose greed and career frustrations resulted in violence towards Maria and Eri. Eri intervened after graduating high school, taking Maria away and sacrificing her own future to raise her. Maria holds deep gratitude towards Eri, joining the Hardy Pro agency only on the condition it imposed no financial burden on her sister. Once her career succeeded, she financed Eri's return to studies. Professionally, Maria respects Nina Hardy for facilitating her entry into showbiz under favorable terms but harbors animosity towards Shun Hardy, the agency president. She orchestrated a scheme to leave his agency and threatened him to prevent retaliation.

In relationships, Maria's bond with Sueharu evolved from initial disdain to admiration and deep affection. She views Kuroha Shida and Shirokusa Kachi as romantic rivals but doesn't consider them serious threats, even suggesting she might temporarily "share" Sueharu while believing he would ultimately choose her. Her determination is encapsulated in the statement: "I won't lose, even if I have to use my body."

Her name carries significance: "Maria" combines characters for "real/genuine," "reason/logic," and "love/affection," while "Momosaka" means "peach slope/hill," reflecting her nickname "Momo" and its association with peach/pink. Her character development involves reconciling her manipulative tendencies with an underlying kind nature, often aiding friends and classmates despite a stoic exterior. Across all media, her arc focuses on overcoming past trauma, pursuing unrequited love, and striving for professional success alongside personal connections.