Misuzu Midorikawa is Lynn Russell's mother, killed shielding her daughter during a car accident en route to England before the main narrative. George Russell, her husband and Lynn's father, concealed her death by claiming Misuzu departed to "a far away place" by "God's will," due to Lynn’s youth and inability to grasp mortality.

Misuzu met George during his business trip to Japan. Her personality mirrored George’s deceased first wife, Frances Russell, influencing his decision to marry her. She raised Lynn alone in Japan for five years preceding their relocation attempt.

Her core aspiration defines the series: she wished Lynn to become a "true Lady," embodying mercy, courage, and nobility. This ideal is symbolized by a golden heart-shaped locket gifted to Lynn, engraved with these virtues.

Though deceased, Misuzu maintains narrative presence through Lynn’s memories and dream sequences. She manifests to encourage Lynn during despair in both manga and anime adaptations, reinforcing her lasting impact on Lynn’s resolve.

Her Japanese heritage critically shapes the plot. The Duke of Woburn, George’s father, rejects Lynn due to her mixed Anglo-Japanese ancestry, reflecting period biases and fueling conflict over Lynn’s acceptance into the noble family.

Beyond the locket, her sole physical legacy is the "Lady’s Key" entrusted to Lynn, representing Lynn’s pledge to fulfill her mother’s wish. Adaptation variations exist: the manga shows George scarcely acknowledging Misuzu’s parents or background post-death, while the anime amplifies her role as Lynn’s spiritual guide during crises.