Age: 14-16
Birthday: November 9
Blood type: A
Height: 161cm
Weight: 42kg

Utau is a 14-year-old junior high/high school student model turned into singing idol.

Utau Hoshina is actually only her stage name, since her actual name is Utau Tsukiyomi, and is Ikuto's younger sister. She is in love with Ikuto and is constantly trying to win his affection, and thus becomes extremely agitated when she notices that Ikuto is interested in Amu Hinamori instead of her. However, she eventually becomes friends with Amu.

Utau was both independent artist (with her hit song, Meikyuu Butterfly) and the vocalist of the indie band "Black Diamond", produced by her manager, Sanjo Yukari, as a method of using the CDs of their music to draw the eggs out of children and make them into X-Eggs. When the plan fell apart, Utau quit Easter Company with her manager and became a singer on her own, without Easter contracting her.

For some time Utau was deeply infatuated with Ikuto, but her feelings were unrequited. In the first Encore chapter, Utau reflects on this a bit and how it used to be the "best thing ever", but now Ikuto had moved on and that how she is lonely now. It can be assumed after Utau's self-reflection that she has overcome her brother-complex.

Utau shares the same competitive personality with Kukai. The two of them have a ramen eating competition in both the anime and the manga. The first Encore chapter is mostly dedicated to their relationship, how it came to be, and Kukai kissing Utau!