Mystic Kai is the fictional character in Dragonball Extreme.
Mystic Kai is a warrior who helps Old Kai and Kibito Kai. He does so because they need his help to fight against the forces of evil invading Earth and their own world. Mystic Kai is from the other world, where he trained himself to use supernatural abilities. Kibito Kai thinks Kid Buu killed all of the Kais, but one had survived. In Mystic Kai's flashback, he was been blown away by Majin Buu into a desert, and he tried to find help, but he fell unconscious. Then he was found by other warriors and taken into other world where he was nursed back to health. He remembers what happened to his fellow Kais, but he's been told by King Kai that Majin Buu has been killed and other Kais are alive.