Rosetta is (possibly) the daughter of Rosalina. She is much younger than most characters, but older than the babies, making her 10-12.
Rosetta looks like Rosalina as a child, but redder hair. She has a white dress and usually goes barefoot. She is also usually seen with a yellow Luma, known as Twinkle.
Rosetta is usually bossy and annoying, but when around her friends she calms slightly.
Relationships with Other Characters
Twinkle, her Luma friend, is the only person Rosetta has majorly interacted with. She usually sees him as annoying, but he does bring out part of her soft side off and on.
Rosetta appears to have a crush on Mario. When they first meet, she teases him for being speechless, but Luigi defends his brother remarking that Mario rarely speaks anyway.
Rosetta (originally) finds Hazel irritating. But towards the end of the game, they become closer friends.
Destello admires Rosetta, and names his ship after her (the SS Rosetta). Destello (along with Twinkle) is in charge of protecting her.