What! I can't change back
Hikaru was at a hamburger store wondering why Hime-chan didn't transform. She was with some of the other girls of the Daichi fan club. One of the other girls had a science fiction book. The title was "parallel world", and when Hikaru saw it, she realized what the magic word for Hime-chan's transformation was. She decides to set a trap for her with the help of a magazine photographer.
Aired 29/01/1993EP 17 - What! I can't change back
Hime-chan no 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.
(Source: Anime News Network)