Misuzu Midorikawa, the deceased mother of Lynn Russell, met George Russell during his business trip to Japan. Her personality resonated with George due to similarities to his late first wife, Frances, forging their connection. Following her separation from George, Misuzu raised Lynn alone in Japan for five years.

Tragedy struck when Misuzu died in a car accident while traveling with Lynn to England for a reunion with George. During the collision, she used her own body to shield Lynn from harm, an act that directly caused her fatal injuries. This event left Lynn hospitalized, initially unaware of her mother's death; George delayed revealing the truth due to her young age.

Misuzu's final aspiration for Lynn was to become a "true Lady," embodying the virtues of mercy, courage, and nobility. This wish became a powerful driving force in Lynn's life. The physical symbol of this promise and Misuzu's legacy, the Lady's Key, was passed down to Lynn.

In moments of Lynn's despair or discouragement, Misuzu occasionally manifests within her daughter's dreams. These dream appearances offer comfort, guidance, and motivation, reinforcing Lynn's resolve to persevere and uphold her mother's ideals. Misuzu's influence persists as a spiritual presence encouraging Lynn's growth.

Adaptation portrayals differ. The manga depicts George eventually marrying Magdalene Waverley despite Misuzu's memory, adding complexity to his character, and references the anguish of Misuzu's parents in Japan after her death. The anime adaptation omits both George's remarriage and the grandparents' subplot, maintaining George's unwavering devotion. Conversely, the anime places greater emphasis on Misuzu appearing frequently in Lynn's dreams as a source of strength, a detail less prominent in the manga.

Her character remains defined by her relationship with Lynn, her sacrificial death, and her enduring symbolic presence as an inspiration for Lynn's journey.