Voiced by: Madoka Yonezawa (Japanese)
Ui is Yui's younger sister, who begins the story as a third-year junior high school student, but later enters Yui's high school the following year in the same class as Azusa. Unlike her older sister, Ui is mature, responsible, and handles household chores well, though she still shares a strong relationship with Yui and has a great deal of love and respect for her older sister. Despite being a year younger than Yui, she is nearly identical to her with her hair down and is even once able to fool the club. She plays the organ, and is also a fast learner, able to learn playing the guitar after a few days' practice. She takes particularly good care of Yui and strives to look after her even at the risk of her own health. Ui is actually considered as the ultimate groupie for her sister's band and supports them with all her heart and occasionally provides a narrative to the story. She eventually joins the light music club along with Jun at the end of the series.