Xenoblade revolves around a special sword called the Monado. The Monado was wielded by an ancient Titan called the Bionis when it fought against another titan called the Mechonis.
Eons after the great battle, the Monado found its way in the hands of the Homs (the humans in the world of Xenoblade). First, in the hands of a hero called Dunban, then in the hands of a young boy named Shulk. The Monado is the only effective weapon agains the metal bodied creatures called "Mechons". The Monado also allows its wielder to see the future, and in turn change it.