THE STAR PRINCESS
Before papa became the Doctor, he told her stories about a star princess. She wandered through the cosmos, until one day, an ouroborus trapped her in a castle made of dead planets. But the star princess escaped, because she was made of light and found a crack between them.
On her last, rainy night, when copper burned in her mouth and sirens wailed, Ai asked her papa if she could become a star, too. He told her she must be a comet instead. So she remained within his castle, staring up at the stars and wondering why?