Ume Matsuzaka, a 24-year-old unmarried teacher overseeing the Rose Class at Futaba Kindergarten, clashes fiercely with Midori Yoshinaga of the Sunflower Class. Outwardly stylish, she conceals her strained finances, living in a cramped, dusty apartment and stretching her budget with noodles and lettuce as months end. She despises her name, "Ume," deeming it unrefined, and demands colleagues avoid using it. Though vocal in criticizing the kindergarten and feigning interest in transferring, she rebuffs outside job offers, quietly clinging to her post.

Her agility, sharpened through dance training, lets her execute mid-air flips to protect her outfits from damage. Prone to sparring with peers and students alike, she masks a pragmatic kindness—most evident when helping Midori reconcile with her fiancé. Romantic pursuits often crumble under comedic interference from her pupils. Past entanglements include Kawaguchi, Tokuro, and Shingo Kakeda, while her sisters, Matsu and Take, hint at a family naming convention she rejects.

Within the film’s plot, she initially allies with the protagonists before betraying them as a spy for the Higures, sabotaging a barrier to enable invasion. This duality mirrors her conflicted nature—self-serving yet inconsistently loyal. Her striking appearance, marked by a toned figure and polished demeanor, draws persistent admirers, complicating her quest to transcend the "low-class" identity her name represents.