The Wicked Blade is a gift from Alfons Fryar to the Princess, following her work in the Wizard's Tower for Alfons' mission in Lesson 6. In Part One v1.40 and earlier the gifted item was the Poisonous Short Sword. It's possible this was changed to include a weapon with acid damage due to problems with Bognar Felaberk during the Uncover the Dhorn Spies quest.