Yume is the youngest sister of the Kuonji siblings, with Miyu and Shinra being her older sisters. She also seems to show signs of being envious of Shinra's fondness towards Miyu. She tries to find her own unique personality and asks the others to make suggestions on what it should be. She is shown to be very sad about her seemingly boring personality, as her sisters and everyone else around her have very distinct and eccentric personalities. She is quite attached to Natose and is her mistress.
Yume is usually shown wearing a school uniform, consisting of a white shirt with blue highlights, a yellow bow around her neck, a short blue skirt, long white socks, and some blue and white tennis shoes. She also wears a hairpin and two yellow bows in her hair. She has fair skin with blue eyes, and pink hair. She has a slim waist and her breasts are average sized.