Jiidon

Legends among jiidons explain that many ages ago, when magic was wilder and of less distinct order, a magic-touched rat consumed the discarded fingernails of a human, and the gods granted that rat the ability to shapeshift into a copy of that human. True or not, jiidons are seemingly normal rats who share the blessing from this story. It's unclear where the first jiidon was born because their descendants live among rat and humanoid populations around the world. In their original forms, jiidons are extremely difficult to distinguish from an ordinary rat and often even finds a home leading its non-sapient kin.

After eating the discarded fingernails of a humanoid, however, a jiidon can assume the shape of the clippings' owner, resembling the subject in all of the obvious and superficial ways, with several subtle differences. Their ears are a little larger and sometimes come to a small point. Their teeth continue to grow for their entire lifetimes, so they must regularly chew on stones, bark, and other hard materials to file their teeth down and conceal their true nature. The whiskers that grow from the sides of their faces also require daily trimming.

Jiidons are mostly harmless, but their powers provoke alarm among those who know of them. Mothers scold their children not to clip their nails after nightfall, lest a lurking jiidon seize a sliver that got lost in the dark. Though as cautious as any rat, most jiidons want nothing more than to transform and take a place in humanoid society. In order to reduce suspicion, they've been known to target those who are unpopular among their neighbors. The gratitude they feel when they do replace a humanoid can sometimes be seen in their actions, revealing the fact that the target has been replaced or endearing jiidons to those who didn't appreciate the original's attitude.

Jiidons from large families will often seek a role that grants them access to nail trimmings, such as a cleaner or doctor, and pass the gift of humanoid form through the family.