The sword of Tranthix

The hero Tranthix made a deal with the devil Laquishta and Laquishta went into his sword. Tranthix gained demonic powers but Laquishta slowly started sucking the life out of him in turn. After Tranthix realised this he used the demonic spell of trapping to trap Laquishta, but got trapped in return. 300 years later a miner goes into a cave searching for fossils and instead uncovers the sword, with Laquishta still inside