Okay, that sword is NOT normal. It was created by a demoniac blacksmith who had been asked to create a weapon able to defeat any ennemy. The Oblivion Sword is, indeed, the most powerful weapon on earth. But there's an huge price. He who uses it shall die shortly. And his soul is damned: it belongs to the sword and will eternally face the slaughters it's used for.
The numerous faces in the sword are the souls of previous users.