In 21XX, Dr. Light's magnum opus, X, is discovered by Dr. Cain. X is the first ever robot with unlimited free will and the ability to evolve like a living thing; his design is used to revolutionise robots into Reploids (called so as derivatives of X's design). However, Reploids hold the power to rebel against the humans, leading to the designation of such rebels as Irregulars and the creation of a peacekeeping organisation called the Irregular Hunters to keep them in check. Things go wrong when the leader of the Irregular Hunters, Sigma, goes Irregular himself and leads the largest Reploid uprising the world has ever seen. This begins the Irregular Wars, in which X and the Hunters struggle for peace against Sigma and his Irregular followers.
