Grand Kai's planet (大界王星, Dai Kaiō-sei)[1] is a planet exclusive to ananime filler saga. This planet is the home of the Grand Kai, the ruler of the galaxies.
After Cell destroyed King Kai's planet, King Kai, Bubbles, Gregory and Goku decided to take a trip to the Grand Kai's planet so that Goku could meet other powerful heroes. After doing so, Goku competes in the Other World Tournament, where he most notably fights against Pikkon. Goku ends the tournament with a draw against Pikkon as both of them touched the ceiling of the tournament stage which ended in a loss on both sides and continues to live and train on the planet for the next seven years.
In the Kid Buu Saga, Kid Buu is shown to appear on the Grand Kai's planet in his search for Goku and Vegeta. King Kai is terrified at the sight of Kid Buu. Unaware of his identity, Pikkon and Olibu seem to enjoy the presence of the pink creature and taunt him.
It does not take long for Kid Buu to get into his destructive ways. The only people aware of his true strengths were King Kai, West Kai, Krillin and Yamcha, who were trembling with fear. When Kid Buu began to power up in order to destroy the planet, Goku and Vegetapowered up at the Supreme Kai's planet which Kid Buu sensed immediately and teleported to that planet, thus saving the planet and the inhabitants in the nick of time.