My Only King(2004)

Boku dake no Ou-sama

In the land of magic, a new king is being crowned. However, a mishap during the ceremonial rite causes the royal crest to be accidentally attached to a normal human, Kazuomi. To protect the crest from any villains who may be after it, Mewt, the cute and brave sorcerer, is dispatched to the human world. There, Mewt must live disguised as a girl, and as "she" and Kazuomi live under one roof together, the two begin to find themselves attracted to each other...

(Source: Juné)