I Help the Protagonist Kill the Villain

Qi Xuan signed a "rebirth" contract before his death. In order to continue to survive, he had to enter various worlds to perform tasks. The mission content is extremely dangerous, including killing villains as an assistant to other protagonists, or killing villains that have been missed in a certain world. Therefore, Qi Xuan once witnessed the destruction of a world with his own eyes, and also faced off against the strongest king in the world...