Tra-Zel-Chromia Medieval AU with Chrome as an exiled Prince in hiding, Travel as a super powerful Magician-in-training, Zel as an over-enthusiastic idealistic Knight.
It's something like, Zel and Travel both train in the kings castle, but the crown prince is horrible and cruel and unfair. (They don't know each other until Travel accidentally shoots a spell out the window turning Zels horse into a dozen chickens or something.) Anyways, the king dies, leaving bad-prince to be king, and Zel decides to look for the lost Prince Chrome, dragging Travel along with her. They get past the traps and enchantments guarding Chrome's tower/castle/prison. But when they finally get to him, he refuses to be king. Zel won't take no for an answer so she basically forces Travel to use magic to get Chrome to cooperate but it backfires causing Chrome to forget everything. So the three have to go on yet another quest to find the power ful sorceress Roxanne to fix the mess Zel made and get rid of Chrome's amnesia.
Sorry, I'm just a huge sucker for AUs :D