The Demon Lord, Mu Yexun, was injured in battle against the Saint, losing his arm. With the Saint's help, he used a ten thousand year old Crystal to create another arm. He never could've imagined, however, that the arm would possess spiritual intelligence and run amok, causing endless troubles. The Demon Lord and his right hand started living together with different objectives in mind — and unexpectely, they slowly develop feelings for each other. However, the Crystal is hiding an unimaginable secret…