In The Paths of Destiny, according to a quest phase titled "The Sword", the blade is exceptional: "light, sharp as a razor, and fits the hand neatly". In the same entry, it is said that the blade "has a destiny of its own. Time will tell what that destiny is". Possibly referencing a sword with a similar name that was given to Lancelot by the Lady of the Lake in Arthurian legends.
Can neither be bought nor sold
Lady of the Lake knights Geralt after he fulfils her wishes, and gives him this blade along with the words: "Take this sword as a sign of my favor. Once the blade of a great warrior, it lay in the depths for ages, awaiting your arrival."There Can Be Only One" in the second expansion for The Witcher 3: Wild Hunt. The secondary quest can only be started if you have completed quests which encompass all five of the chivalric virtues. If you have not completed a quest covering that value, you will be told which chivalric value you are missing.
After Geralt completes Hermit's tasks and defeat him in trial of combat then the Lady of the Lake appears and she says that: "Forget not that you are a man right and honorable, devoted to doing good. And for these reasons you received the blade. Now bear it. And I trust this time you shall not lose it..."