A young Rosalina finds Luma in a space ship that resembles the Starshroom. Rosalina waits with Luma for Luma's mother who was apparently coming for him on a comet. Rosalina gets tired of waiting so the pair fix up the spaceship and set off. Together, they collect star bits to sustain themselves, and along their journey, they come across a comet. Luma gets excited and they land on the comet. Luma's mother was no where to be seen, however they discover star bits and supplies from which they can build a home on the comet. One night, Rosalina has a dream about her mother leaving her, promising to watch over her as the sun, moon, and stars do. She awakes crying over the grief of missing her mother, and Luma joins in. Eventually, they complete their home on the comet, though they acknowledge that it is quite large for just the two of them. One day, an apricot-coloured planet appeared from which another luma of the same colour came. Both lumas began excitedly shouting "My mama! My mama!", while dozens more lumas came from the planet. They all shouted "My mama! My mama!" as they circled around Rosalina who becomes the adoptive mother of the lumas. Many days pass, and she finds herself reminiscing about her home planet. She recounts the stories about how she would stargaze with her father on a hill, and sled down the hill in the winter with her brother. Upon recounting stories of her mother, she once again breaks down, homesick and distraught. Rosalina admits that her mother isn't watching over her from the stars, but rather that she is sleeping under the tree on the hill, revealing that she passed away and is buried there. After several days of crying, the first Luma decides to thank Rosalina for her love and care by transforming into a comet, and helping propel their home back to Rosalina's home planet. Realizing that she herself must now take on the role of mother to all the Lumas on the comet, she rises into the role and cares for them all as a family, reminiscing about how one day each of them will grow up and move on to their own destinies and how she would smile each time because; "-that's what makes a mother happiest". Still missing her home planet, Rosalina resolves to visit the planet every century on the comet, allowing her to sleep in her favourite spot under the tree.
- The Storybook was not planned to be in the game. One of the developers made it in their spare time.
- After all 120 power stars are collected, in the secret ending, there is a mossy spaceship in the Gateway Galaxy. It is assumed to be the same one Rosalina and Luma used.
- Like in the storybook, there is no glass in the windows.
- A book with similar appearance appears in Super Mario Galaxy 2. However, this book tells the story of Super Mario Galaxy 2 itself.