The world in which the three kings live is ultimately divided.
The Spirit King of the Soul Society, the True King of the Human World, and the Void King of Hueco Mundo. The three were originally wedges between the existence of the world, but the Void King coveted the True King and exterminated the royal family, but he did not expect that there would be such a disaster in the future.
It's too late to regret, everything is out of control.
Because of that war, they were separated by life and death.