Miu Takanashi, the 10-year-old second eldest of the three Takanashi sisters and a fifth grader, possesses distinctive blonde hair from her Russian-descended biological mother. Her biological father left before her birth, making Shingo Takanashi her stepfather. After her parents disappeared, she moved in with Yuuta Segawa, calling him "Oji-san," alongside sisters Sora and Hina.

Precocious and outgoing, Miu exhibits a strong interest in fashion, cosmetics, and traditionally feminine activities. Her popularity among school boys sparks jealousy and open mockery from female classmates, though she maintains at least one supportive friendship with a girl who defends her. She frequently emphasizes the importance of "delicacy" in social interactions. Her preference for older, masculine men emerges early, accompanied by particular curiosity about Yuuta's romantic life, hinting at her developing affection for him.

Her character development intensifies when her biological mother, Sasha, reappears in volume 4 offering to take her to Russia; Miu chooses to stay with Yuuta and her sisters, solidifying her commitment to their family. Sasha later returns in volume 8, becoming recurring. By volume 17, Miu enters junior high school and pursues a singing idol career, leveraging her social popularity and confidence.

Within the family, Miu acts supportively, recognizing Sora's crush on Yuuta and encouraging her to confess independently. This supportive role, however, masks her own emotional struggles; her tendency to prioritize others' needs serves as a coping mechanism for unresolved personal issues, reflecting deeper complexity beneath her cheerful exterior.