Shichiseiken

One could say, the true antagonist behind the events in movie 5, Curse of the Sacred Sword. Its a sword that was created from the bloodshed of three warring kings that tried to get the hand of a maiden thus absorbing all negative energy around it. The maiden however sacrificed her life to stop the warring kingdom and, in their sorrow, the kings sealed the sword away. Years later though Saga during a pirate attack, found the sword in a crypt he and his girlfriend, Maya, were cornered in and used it out of desperation to save her. However the sword's evil influence possesses Saga and brainwashes him into trying to rise to full power. Using its power to posses a nearby Marine dojo to do its bidding and, sensing Zoro nearby, having Saga contact him for it's plans to get rid of sacred jewels that could seal it's evil power. However Luffy manages to find these jewels and the Straw Hats, with the help of Maya, are able to enact a ritual that will suppress it power. The sword tries to stop this and nearly succeeds, initially being beaten by Luffy once then merging with Saga's body which makes it near unstoppable. Even able to disperse Maya's barrier on it own. However its finally stopped when Zoro appears and calls to Saga's consciousness, challenging him to a sword duel. Zoro manages to slash at Saga but only destroys the sword's influence allowing Saga to live.