The legendary saber of Brand. It is the Day Sword.
The mighty Werewindle is 115% better than a typical shortsword (295% better than typical dagger), partly because its faster speed. You will take quite some skill with backswords to use it well. It gains extra effectiveness with your light spell casting skill. The back of the weapon provides some defensive value too. Take care, this is one-of-a-kind.
Found as curved sword.
Note: Each hit causes extra lighting damage (works with blessing enchanted version)