Momo Shinozuka, a second-year Samejima Academy student, balances her roles on the student council and public morals committee with unyielding adherence to rules and traditional values. Though she enforces regulations with stern efficiency, her disciplined exterior masks private loneliness, softened only by her secret affection for teacher Gotō—the catalyst for her committee service after he praised her integrity.

Her solitary routine fractures upon encountering free-spirited underclassmen Chio Miyamo and Manana Nonomura. Initially clashing with their chaotic antics, Momo reluctantly becomes entwined in their adventures, earning the title "Momo-senpai." Their influence nudges her toward tentative camaraderie, fraying the edges of her rigid worldview.

Beneath her authoritative persona lies a timid, emotionally vulnerable soul who retreats into tearful anxiety when overwhelmed. Paradoxically, mint chocolate sparks a vibrant, gleeful side, contrasting her usual austerity. This duality mirrors her struggle to reconcile duty with latent desires for connection.

Driven by a need to impress Gotō, Momo initially channels all energy into committee work. Yet her growing bond with Chio and Manana pulls her into impromptu escapades, exposing her to spontaneity and incremental social growth. While perplexed by their unpredictability, these interactions chip at her isolation, forging fragile bridges between her moral certitude and their unorthodox warmth. Her journey traces a quiet evolution from uncompromising enforcer to someone tentatively embracing the messy complexities of friendship.