Xenoblade Chronicles

From the introduction:

Long ago, the world was nothing more than an endless sea cloaked in a boundless sky, reaching as far as could possibly be imagined. Then two great titans came into existence; The Bionis and the Mechonis. The titans were locked in a timeless battle, until at last, only their lifeless corpses remained.

Eons have passed. Now, the vast land stretching across the remains of the Bionis is under attack from a relentless force known as the Mechon. Only one weapon is able to reliably slay this mechanical menace - The Legendary Sword of the Bionis, the Monado.