Serendipity chanced upon her form. The daughter of fate and chaos, she is generally an entity that brings good luck if you keep your eyes and your mind open enough to find her work. She is usually only noticed after the fact, but she is a huge fan of mortals and tries to aid them as much as she can.

In the beginning, she was shapeless. By chance, a terminally ill child manages to see her and insisted that her crayon drawing was what Serendipity looked like. Serendipity took that shape and kept it ever since, making it a wonder if she didn't spread the mouse shape rather than her looking like a mouse. As for the child, she gave the family food poisoning which, luck would have it, also improved the child's condition. A doctor took notice and was able to make a slightly less unpleasant medicine as a result and the child lived.

Despite her size, Serendipity if a cosmic force to be reckoned with, and she will not hesitate to meddle in everything if she must.