Overwhelmed with fear of losing his qualification to remain in the world, Durendal panically exclaimed, "Are you not going to regret your decision, young man?! Once you erase me, you will also erase Durendal!"
Sword Soul was the essence of a good sword. It possessed the unique ability that made it better than any other swords because the wielder whom the Sword Soul was originated from had nurtured it throughout his life.
Erasing a Sword Soul out of a legendary sword was the same as taking away the abilities of the sword that made it special in the first place. Doing so would only result in giving one an ordinary sword that had no extraordinary aspect.
In Durendal's case, Basil would no longer be able to enjoy its peerless sharpness or the Hidden Abilities, which he hadn't explored yet. Durendal would be a mere well crafted Claymore that was sturdier than most.
