The oldest of the three Nonohara sisters, Aiko is someone who her younger sisters  (Himeko in particular) look up to a lot. She is very feminine and domesticated, two things that Himeko is desirous of for herself at the beginning of the story, and is commonly thought of to be very beautiful by other characters in the series.  She finds love early on in the story.

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.<br><br>
(Source: Anime News Network)

Princess Erika of the Magic Kingdom must test out a magic item that she created for a year on her human world doppelganger before she can qualify for the throne. Her look-a-like happens to be Himeko, a tomboy who worries that her boyish looks and attitude are ruining her chances with the boy she is in love with. Erika gives Himeko a ribbon that allows her to transform for an hour into anyone she wants, but if she exceeds the time limit, or if anyone finds out, she will be stuck in that form for the rest of her life. 

Aiko Nonohara