Yumi Morita is Mayu Morita's mother and her primary instructor in proper manners and communication etiquette. She frequently draws these lessons from her own experiences confronting her husband about his habitual flirting and consistent pattern of spending nights out, actions which trigger her anger. During these interactions, Yumi often projects her frustrations about marital misunderstandings onto the advice she gives Mayu. This dynamic contributes to Mayu's tendency to overanalyze social interactions, as the guidance stems from avoiding miscommunication within tense domestic situations.

Despite recurring conflicts with her husband, their relationship features patterns of reconciliation, characterized by zealous make-ups following jealous disputes. Yumi maintains a traditional presence, consistently depicted wearing a kimono, aligning with the Yamato Nadeshiko archetype of a dignified, ideal Japanese woman. Her demeanor shifts notably when addressing her husband's behavior, revealing a formidable and intimidating aura often accompanied by visible frustration like cross-popping veins. This aspect underscores the contrast between her generally calm disposition and the intense reactions provoked by her husband's actions. Yumi remains a significant influence on her daughter's approach to social interactions, though her advice is intrinsically intertwined with her own marital challenges.