Mitsuki Sonoda is a supporting character in the anime Sakura Trick. She is the older sister of Yuu Sonoda and serves as the president of the student council at Misato West High School during the first year of the main characters. In her role as student council president, Mitsuki is typically reserved, dignified, and regarded as a respected leader whom others look up to. However, her composed exterior easily crumbles when she is around Haruka Takayama, toward whom she becomes noticeably flustered and clumsy.

Mitsuki has a tendency to fantasize frequently, often without being fully aware that she is doing so. She shares certain traits with her younger sister, such as wearing flower-shaped hair ornaments and having a fondness for matcha-flavored sweets. Physically, she is of average height with long blonde hair and green eyes.

Her motivations are largely tied to her sense of responsibility as student council president and her protective, if sometimes strict, attitude toward her sister. She initially becomes suspicious of the relationship between Haruka and Yuu after witnessing them kissing, which adds tension to her interactions with them. At the same time, Mitsuki develops a one-sided crush on Haruka, which she struggles to reconcile with her professional image and her role as an authority figure. Her growing feelings for Haruka often leave her flustered and unable to maintain her usual composure.

Mitsuki's key relationships include her sister Yuu, whom she cares for but whose secret romance causes her concern, and Haruka, toward whom she harbors hidden romantic feelings. She also works closely with Sumi Otokawa in the student council, with Sumi acting as a confidante who helps Mitsuki navigate her emotions and responsibilities.

Throughout the series, Mitsuki experiences a degree of personal development. She begins as a strict and somewhat suspicious figure but gradually becomes more supportive of the younger girls, even as she remains largely unaware of the full extent of their romantic involvement. Her arc involves learning to balance her professional duties with her personal feelings, though she continues to struggle with her unrequited crush on Haruka.

Notable abilities or traits include her leadership skills as student council president, her tendency to daydream without realizing it, and her overall dedication to upholding school rules. Despite her stern demeanor, she is soft-hearted at her core, which is revealed through her vulnerability around Haruka and her eventual willingness to support the relationships of those around her.