Miku Sugisaki is a student in class 6-3 at Kamohashi Elementary. She is a boisterous and preppy girl whose primary role in the story is that of a rival to one of the Marui triplets, Mitsuba. Her background is one of relative wealth; she comes from a family with comfortable means and often flaunts the latest fashionable accessories, such as a modern mobile phone and high-end school supplies, a stark contrast to Mitsuba's more modest upbringing.

Miku's personality is marked by a fierce competitive streak and a strong dislike for Mitsuba. She is constantly trying to outdo or degrade her rival, whether in academic matters, social standing, or physical attributes such as bust size. Despite her animosity, she exhibits an obsessive tendency, notably taking hundreds of photographs of Mitsuba. Her motivation is driven by the desire to prove her superiority and to humiliate Mitsuba whenever possible. This rivalry is the central axis of her character, and she actively seeks opportunities to belittle her classmate.

In the story, Miku functions as a supporting antagonist of sorts, providing recurring conflict and comic tension. Her key relationship is with Mitsuba, but she also interacts with other classmates, though those connections are less developed. There is little evidence of significant character growth over the series; she remains consistently antagonistic toward Mitsuba, and her behavior does not undergo a meaningful transformation. Her notable abilities include a knack for leveraging her family's wealth to appear more fashionable or advanced than her peers, as well as a sharp tongue and a willingness to taunt. She is not shown to have any supernatural or extraordinary skills; her influence stems from her social and economic one-upmanship rather than any personal talents.