King Kai's planet (界王界, Kaiōkai) is a planet located in the Other World. It is home to King Kai, ruler of the North Galaxy, as well as to King Kai's pets: Bubbles and Gregory. Even though the planet is relatively small, it has gravity that is 10 times that of Earth's, allowing for more intense training (clearly seen through Goku's struggle to even stand up). In addition, the planet carries apple trees, of which the apples in question, when dropped, would burrow down into the ground.
After Goku sacrifices himself for Piccolo to kill Raditz, he is taken to the Check-In Station by Kami. Kami asks King Yemma to allow Goku to travel down the Snake Way and train with the legendary King Kai, so that he will be prepared to battle the Saiyans when they arrive on Earth in one year. King Yemma accepts and Goku spends many months running on Snake road, heading toward the planet. Upon arrival, Goku's skills are put to the test, he was assigned to catch Bubbles (which proved a daunting task considering the gravity) and to hit Gregory with a hammer (which was fairly hard to hold let alone swing). He passes these tests and is permitted to receive King Kai's training. In the next few months, Goku masters the Kaio-ken technique and the deadly Spirit Bomb, moves that will be essential in his battle against the Saiyans. Afterwards, the fallen Z Fighters: Yamcha, Tien Shinhan, Chiaotzu, and Piccolo are given permission to keep their bodies, and travel down Snake Way to receive training with King Kai while their friends are dealing with Frieza on the planet Namek. Goku later visits the planet during the ten day wait for the Cell Games to ask for directions to New Namek, and was also summoned by King Kai to deal with a Super Saiyan that destroyed the South Galaxy.
The next time the planet is actually visited in the main story is when Goku teleports Cell to it as he is about to self-destruct. This kills King Kai, Bubbles, Gregory, and even Goku. Cell manages to survive, and returns to Earth, only to be finally killed by Gohan. King Kai, his pets, and Goku then all travel to Grand Kai's planet. Due to Cell's self-destruction (and thus King Kai's death), the space pirate Bojack and his gang of Galaxy Soldiers were unleashed, leading up to the events of the movie Dragon Ball Z: Bojack Unbound.
- Apple trees
- King Kai's house
- King Kai's 1957 Red Chevrolet Bel Air Hardtop (when he gets bored, King Kai likes to drive around the planet in this car)
- King Yemma – Travelled to receive training.
- Goku – Visited numerous times throughout the series, but mainly to receive training to battle the Saiyans after he sacrificed himself to have Piccolo use the Special Beam Cannon on Raditz.
- Raditz – Killed by Piccolo's Special Beam Cannon due to Goku's sacrifice. Was given a special invitation by King Kai so Goku could be assured that his training is helping him (Budokai Tenkaichi 2 only). Was later given a special invitation by King Kai again, alongside Nappa, to assure one of his students that his training was indeed helping him. This time, the student in question was Piccolo (Legend of the Super Saiyan).
- Nappa – Killed by Vegeta's Galaxy Breaker. He and Raditz were given a special invitation by King Kai so Piccolo could be assured that his training is helping him (Legend of the Super Saiyan only).
- Piccolo – Killed by Nappa after protecting Gohan from the Saiyan's Bomber DX.
- Tien Shinhan – Died after giving off all his energy in an attempt to kill Nappa.
- Yamcha – Killed by a kamikaze Saibamen.
- Chiaotzu – Blew himself up in an attempt to kill Nappa.
- The Ginyu Force (barring Captain Ginyu) – Killed on Planet Namek by Goku and Vegeta. Were given a special invitation by King Kai so his students (Yamcha, Chiaotzu, and Tien) can be assured that their training is helping them.
- Cell – Forced there after Goku used Instant Transmission in order to save the Earth from Cell's self-destruction.
- Olibu and various other northern galactic heroes – All died under unknown circumstances (however the only one heard of was Olibu).
King Kai's planet is visited in Dragon Ball Z: Kyōshū! Saiyan, Dragon Ball Z: Legend of the Super Saiyan, Dragon Ball Z: Goku Hishōden, Dragon Ball Z: The Legacy of Goku, Dragon Ball Z: Harukanaru Densetsu, and Dragon Ball Z: Attack of the Saiyans.
It is seen during King Kai's appearances in Dragon Ball Z: Goku Gekitōden, Dragon Ball Z: Super Gokuden: Kakusei-Hen, Dragon Ball Z: Budokai, Dragon Ball Z: Budokai Tenkaichi 2, and Dragon Ball Z: Infinite World. The planet is seen in the background of the Snake Way stage in Dragon Ball Z: Taiketsu.
|Planets||Grand Kai's planet • King Kai's planet • Planet Kaishin • Sacred World of the Kais • Heaven|
|Locations||Cave of the Ancients • Check-In Station • Demon Realm • Freezing Tundra of Hell • Furnace of Eight Divisions • Grand Kai's mansion • Hell • Princess Snake's palace • Other World Stadium • Sugoroku Space • Yemma Forest|
|Roads||Battlefield Royale • Snake Way|