Misuzu Midorikawa, the Japanese mother of Lynn Russell and second wife of George Russell, Viscount of Marble, raised Lynn alone in Japan for five years following an unspecified separation from George. Deeply devoted to her daughter, she sacrificed her life protecting Lynn during a car accident en route to England, an event preceding the main narrative.

George concealed her death from the young Lynn, claiming Misuzu had gone to a "faraway place by God's will." This absence became a central motivator for Lynn, who vowed to honor her mother's wish for her to become a "true Lady" embodying mercy, courage, and nobility, driving Lynn's actions throughout the series.

In the manga, Misuzu's parents express profound anguish over her death and separation from Lynn, a subplot absent in the anime. The anime also streamlines her legacy, omitting manga elements like George's subsequent marriage plans or his death to focus on her idealized influence.

Posthumously, Misuzu appears in Lynn's dreams during hardship, offering encouragement as a spiritual guide. Her keepsake, the Lady's Key, remains with Lynn as a tangible symbol of their bond and Lynn's promise.

Adaptational differences exist: the manga depicts her family's grief starkly, while the anime emphasizes her positive motivation without exploring family trauma. Her background as a non-noble Japanese woman indirectly influences Lynn's struggles for acceptance within English aristocracy, though Misuzu herself is not depicted interacting with that society.