The Universes Assassin

The Universe has created may different things to keep itself in balance, for example, Human heroes have been created to hold off both heaven and hell. But with everything beofre me failing, the universe decided to birth me on the planet that was causing the most issues. This planet is called Earth and thousands of Demons, Angels, Gods and all kinds of monsters run amok here. My job is too pacify these races and if that fails, I'm to become the universe's instrument of death. I have been given a device that will allow me to trade in my experiences on the planet for new abilities that will help me in my quest to bring back the balance.