King Kai's planet

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.

Overview
This planet is the home of King Kai. Its most notable feature is that it's gravity is roughly ten times the strength of Earth, making it an ideal training ground. The planet used to be about 100 times that of its current size, although it is unclear if this implies a higher gravity, but given the planets peculiar "size to gravity" ratio, it likely was the same. The planet contains nothing but a grassy surface, a half dozen or so trees (some of which bare fruit), a road that circumvents the planet, King Kai's house, his car, a well, and some other small building. The God of Destruction, Beerus had visited King Kai's planet at least once prior to the events of Dragon Ball Z: Battle of Gods. During his visit, Beerus and King Kai played a game (either a car racing video game or a "spirited game of hide-and-seek" depending on the version). Upon Beerus's defeat, the God destroyed the planet, leaving it significantly smaller.

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 [http://dragonball.wikia.com/wiki/Unforgivable! 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 are unleashed, leading up to the events of the movie Dragon Ball Z: Bojack Unbound. In the movie Dragon Ball Z: Battle of Gods and Dragon Ball GT, King Kai's planet is shown to have been brought back. In Battle of Gods, the God of Destruction Beerus tracks down Goku, the Saiyan who defeated Frieza, and accepts the challenge from Goku to see how strong he is. When he arrives on the planet, the God of Destruction complains that King Kai's planet is so small, but his attendant Whis reminds him that he is the reason it is so small for destroying it when getting mad after losing at hide-and-seek.

Landmarks

 * 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)
 * Well

Known residents

 * King Kai
 * Bubbles
 * Gregory

Known visitors

 * King Yemma – Traveled 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 theSpecial 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 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, Sarta, Mijorin, and various other northern galactic heroes – All died under unknown circumstances (however the only one heard of was Olibu).
 * Beerus – Came by to visit King Kai, and ended up destroying the original planet. He revisited many years later and fought Goku.
 * Whis – Came to the planet with Beerus.

Video games
King Kai's planet is visited in ''[http://dragonball.wikia.com/wiki/Dragon_Ball_Z:_Ky%C5%8Dsh%C5%AB!_Saiyan 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.

King Kai's planet is a playable battle stage in Super Dragon Ball Z and Dragon Ball Kai: Ultimate Butōden.