星咲 天音

Occupation: Up-and-coming idol
Activities: Book and art club
Favorite things: Protagonist, ice cream
Hobbies: Bathing (with protagonist), reading, drawing
Special skill: Delusions of grandeur
Problem areas: Fear of ghosts 
The protagonist’s younger step sister, a girl who has dreamed of becoming an idol like her mother from a young age.
Her grades in school are top notch, and she is regarded for her beauty. However, she still has a long way to go. 
She loves her step brother, the protagonist, and takes baths with him in the onsen (among other things).
Her measurements grow up to 92(H)-53-84