Nanako Yamamoto teaches at Hanamaru Kindergarten, guiding the first-year Peach Class. She possesses light brown hair flowing past her shoulders to her back, wide brown eyes, and often wears a bow in her hair. Her gentle, patient, and nurturing nature shines through with her young students, like when she calmly cleans up after Anzu helps her instead of scolding the child. Practical skills, including sewing, allow her to mend Naozumi Tsuchida's apron and repair Koume's stuffed panda-cat doll.

Initially, Nanako remains completely unaware of romantic advances directed at her, particularly Tsuchida's affection. She doesn't understand why men would develop feelings for her, though she easily recognizes Hanamaru-sensei's crush on her younger sister, Mayumi Yamamoto. This contrasts sharply with her perception of others' romantic situations. Mayumi, who works part-time for a manga publisher, shares a close bond with Nanako. Mayumi understands her sister's obliviousness and sympathizes with Tsuchida's struggle. Both sisters share a tendency to miss romantic cues aimed at themselves, as Mayumi is equally unaware of Hanamaru-sensei's feelings. Their parents are noted for having a poor sense of direction.

Across the series, Nanako develops. Her obliviousness shifts when she mistakenly believes Mayumi and Tsuchida are dating, triggering her own love epiphany. This leads to her reciprocating Tsuchida's feelings, resulting in a romantic relationship. The kindergarten children actively encourage Tsuchida to confess, facilitating this outcome. Their romantic arc concludes with them maintaining a long-distance relationship after Tsuchida relocates.

Her surname Yamamoto (山本) combines "mountain" (山) and "base, root, origin" (本). Her given name Nanako (菜々子) uses characters for "vegetables/greens" (菜) and "child" (子), interpreted as a pun on "Yamato Nadeshiko," symbolizing the ideal Japanese woman and reflecting her character. Her birthday is May 12, aligning with the Taurus zodiac sign.