Muramasa(Scooby-Doo! and the Samurai Sword)

According to legend, Masamune was hired to create a sword of great magical power by a ronin. He was able to do this in one year, but his evil apprentice Muramasa secretly offered to make one in six months. When Muramasa delivered this sword to his customer, evil entered into the ronin and he became the Black Samurai. The cursed sword became known as the Sword of Doom.