Rosalina's story begins when she meets a young Luma in a rusted spaceship, where they rebuild spaceship to go search for the Luma's mother. They traverse through the space, encountering comets, asteroids, and Star Bits. Rosalina then starts to miss her mother, but the two begin to build a new home that would eventually become the Comet Observatory.

As she and the Luma build the home, Rosalina takes more Lumas under her wing. After they see their 100th comet, Rosalina looks back at her home planet, which then causes her to feel greatly upset and homesick, and then comes to terms with the fact that her own mother is dead.

The young Luma who traversed with Rosalina tells her that her mother is always part of her, and then transforms into a comet that can traverse to Rosalina's home planet. Rosalina then declares that she and the Lumas are her family now, and goes back to her home planet every once in one hundred years.

Rosalina is a generally wise, kind, and a mature woman. She has an intimate knowledge of the universe and cares deeply for the Lumas, where she assumes the role of the total caregiver for them. Her outward strength and inner sorrow are likely due to the loss of her mother. Rosalina is calm and reserved, and often takes pauses when she explains how the universe works. Rosalina can be a little bit more upbeat and joyous, occasionally shouting and cheering, though still mostly keeping her introverted nature.

She gets homesick and misses her mother dearly, to the point where she cries about losing her mother.