Mika Uesugi, later known as Mika Seguchi after marriage, is the elder sister of Eiri Yuki and Tatsuha Uesugi, and the wife of Tohma Seguchi, the head of NG Records. She comes from the Uesugi family, which operates a Buddhist temple in Kyoto, and her father is a monk. Mika is described as sophisticated and elegant, with long brown hair and blue eyes, and she bears a strong physical resemblance to her brother Eiri. Her demeanor is often cold and authoritative, yet beneath this exterior she is deeply protective of her family, especially Eiri, for whom she cares so deeply that she would give almost anything for him.

Her primary motivation throughout the series is the well‑being of her brother and the preservation of family ties. Early in the story, she attempts to force Eiri to visit their dying father by bribing Shuichi Shindo with her own husband, Tohma, demonstrating a willingness to use manipulation to achieve what she sees as necessary family obligations. Over time, her role evolves into that of a stabilizing force who bridges the gap between the Uesugi family’s traditional expectations in Kyoto and Eiri’s independent life in Tokyo with Shuichi. She is more understanding of Eiri’s lifestyle and his relationship with Shuichi than either her father or her younger brother Tatsuha, though her feelings remain mixed – she both supports and questions the relationship.

Mika’s key relationships are with her siblings and her husband. With Eiri, she acts as a caring but occasionally overbearing older sister who wants to see him happy and reconciled with their father. Her bond with Tatsuha is that of an elder sibling, but their personalities differ. Her marriage to Tohma Seguchi is portrayed as formal and somewhat distant; Tohma is unfailingly polite to her, referring to her with honorifics, and his devotion to Eiri often takes precedence over their marital affection. In the manga, there are hints that Mika may be expecting a child, which adds a new dimension to her role. She also interacts with Shuichi, initially using him as a tool but later developing a nuanced, if not fully approving, stance toward his place in Eiri’s life.

Mika’s development is subtle: she moves from a mostly manipulative and commanding presence in the first volume to a more supportive family member who accepts Eiri’s autonomy and his bond with Shuichi. Her notable abilities include a sharp intelligence, strong negotiation skills, and a talent for navigating both high‑society circles and the music industry through her husband. She is observant and knows how to assert her authority when necessary, making her an effective intermediary during family crises. While she does not undergo a dramatic transformation, her gradual acceptance of Eiri’s choices and her own potential motherhood mark the small but meaningful changes in her character.