<Sky's End>, a sword forged by a celestial by mysterious means, using the corpse of a unique three-star class beast. The power of wind and storm flowed through the sword's body, its edge exuding a seductive yet deadly radiance. It was, without a doubt, an exceptional weapon.
When Desmond received the sword from Katya, she mentioned something about the difficulty of creating such an artifact, which Desmond didn't understand until much later. Katya was talking about artifacts with spirituality, special relics capable of developing beyond the limits defined by her birth.
In addition to its inherent quality of growth, a spiritual weapon also had characteristics and abilities that gave them spirituality. In the case of the sword, <Sky's End> was created with the carcass of Skaylos the Stormbringer, so it was expected that the sword would have related abilities engraved on it.