Kuni Yashiro rules as matriarch and owner of Sakata’s Kaga-ya rice dealership. Her initial skepticism toward Oshin—fueled by Oshin's association with army deserter Shunsaku—dissolves when Oshin rescues Kuni’s granddaughter Kayo from a falling utility pole. This act cements Oshin’s acceptance into the household, overriding objections from Kayo’s mother regarding a servant’s social standing.

Recognizing Oshin’s potential, Kuni mentors her directly in reading, writing, abacus arithmetic, and the Japanese tea ceremony. She positions Oshin as a role model for Kayo, aiming to instill responsibility in her disinterested granddaughter, who resists inheriting the family business. Kuni orchestrates marriage prospects for both, securing Oshin an introduction to a wealthy Sakata family’s second son. This match collapses due to Oshin’s hidden affection for Kouta Takakura.

Kuni confronts Kayo’s rebellion against tradition when Kayo flees Sakata for romance, fracturing their relationship. After Kayo’s sister Sayo dies, Kuni arranges Kayo’s marriage to Masao—an Osaka rice merchant’s son and Tokyo Imperial University graduate—to fortify Kaga-ya’s future. Amid these tensions, Kuni’s heart attack and declining health trap a reluctant Kayo in Sakata.

Her leadership merges pragmatism with compassion: she grants Oshin leave to tend her dying grandmother and supports her during Sayo’s funeral, transcending employer-employee boundaries. As an elder, she embodies the "Cool Old Lady" archetype, wielding influence through authority and authentic care. Kuni’s decisions consistently prioritize Kaga-ya’s stability and generational continuity, navigating intricate family dynamics with resolve.