Escaflowne

One Will Wake It. One Will Destroy It.

From the introduction:

Is this a Dream? Or a vision? No, this is reality. Though, I suppose a traveller like yourself is the last person who’d need to hear such words. Say what you will about the choices you’ve made to bring yourself this far, it was nothing less than destiny itself that led you to the glistening fields of Gaea. This strange, fantastical world, where the ocean drenched rock you might have called Earth hangs in the sky as this planet’s own moon.