Hime-chan's Ribbon.

Erika, the princess of the Magic Kingdom has come to Earth in order to find a human girl who looks just like her. That girl turns out to be Himeko Nonohara, a tomboy's tomboy. Erika must give Himeko a magical item she has created in order to prove her worth as a successor to the crown. Himeko must test this item, a hair ribbon that allows her to transform into any other person she sees, to see if it is worthy. The series follows Himeko's adventures and her budding romance with Daichi, the boy who discovers her secret.