The protagonist of Sega's superstar RPG World Destruction is a boy named Kyrie who joins a secret organization called the World Destruction force, whose goal is not to save the world from destruction, but to cause the world to end. Kyrie was apparently a normal student until one day when he just up and joined a shadow organization devoted to the destruction of the world.
You'd probably want to destroy the world too if the world you lived in was populated by monsters who enslaved humanity. You'd probably also just want to try your unique world-ending power once. Famitsu's got lovely screens of this vaguely morbid game!