With Piccolo in hiding, five peaceful years pass by. A UFO land on the earth, and a man jumps out. He is searching for Kakorat. Piccolo senses the great power, and goes to investigate. The alien does a scan on Piccolo, realizing that his sentou-ryoku is 322. Piccolo attacks the alien, but they have no effect at all. In disgust, the alien leaves to find Kakorat. Piccolo can bear being humiliated, so he goes to search for the Saiyan-jin's help.
At Kamesennin's house, everyone is having a reunion. Kuririn asks Bulma where Yamcha is, and Bulma says that they broke up. Everyone hears Gokuu's voice, and run outside. Instead, they meet Gohan, Gokuu's son. Gohan is four years old, and still has his tail. This means that if he sees the moon, then he will turn into a were-monkey. Gohan's hat has the Dragonballs #1 - #6 on it. Gohan wears the ball which matches his age. The alien lands at the house, and asks for Kakorat. Kuririn tells the alien to leave, when Gokuu notices that the alien has a tail, meaning that he is a Saiyan-jin. The alien tells Gokuu that he is Kakorat. Gokuu denies this and says that he's Son Gokuu. But Gohan's tail is proof that Gokuu is a Saiyan-jin. The alien is Raditz, Gokuu's older brother. Saiyan-jins are born on the planet Vejiit and have fighting blood inside them. Everyone tells Raditz to leave, and he just laughs at them. Raditz kidnaps Gohan, and throws Gokuu. Raditz tells Gokuu that he has two choices: to fight Raditz, or to return to the planet Vejiit. Also, Raditz want's Gokuu to bring 100 corpses, otherwise Gohan dies.
Gokuu calls for Kintoen, and chases Raditz. They use the Dragon Radar to track down Raditz (Gohan has the Dragonballs on his hat). Kuririn and Kamesennin go to get Tenshinhan and Yamcha, while Piccolo appears. Gokuu wants to know why the Demon King has come back, and Piccolo says that this is his planets to terrorize, not the aliens. So Gokuu and Piccolo alliance together.
Raditz places Gohan into the space capsule, and is alerted that Gohan has a sentou-ryoku of 710. Raditz can't believe this and tells the "shit-brat" to stop crying. Raditz then find a power rating of 322 and 334 approaching (Gokuu is 334). Piccolo and Gokuu take of their heavy clothing (they both used it for training), and their power rating jumps.
They fight, and the hero's are shocked that Raditz can easily fight against both of them at the same time. Piccolo starts up Makankousappou, while Gokuu distracts Raditz with a Kamehame-ha. Raditz avoids both blasts, and then starts beating up Gokuu and Piccolo. Gohan escapes from the space capsule, only to see is father being punched around the place. Gohan gets angry, and his power level reaches 1300. Raditz attacks Gohan, and is about to kill him when Gokuu grabs Raditz. Piccolo shoots Makankousappou again, and kills both Gokuu and Raditz. As Raditz is dying, he tells the others that two more powerful Saiyan-jin's are going to earth to destroy it in a year. Piccolo promises to get the Dragonballs and wish Gokuu back to life.
Meanwhile, on another planet, Nappa and Vejiita hears about the Dragonballs (the power scanner is also a communicator). Vejiita wants the Dragonballs so that he can become the legendary Super Saiyan-jin.
Everyone else meets back at Kamisama's house. Piccolo gives the power scanner to Bulma, and gets her to learn how to use it. Kamisama takes Gokuu's body to heaven, while Gohan follows Piccolo for intensive training for the upcoming battle with the two Saiyan-jins.
Gokuu is then told by Enmadaiou-sama to go the Snake Road, where he will eventually meet Kaiousama. Kamisama tells Gokuu that he has to travel one million kilometers on the snake road to arrive at Kaiousama's house. If Gokuu doesn't have a pure heart, then he will fall through the clouds, and into hell. Gokuu is unable to use Bukuujutsu to fly down the road, so instead he walks. Uranai Baba tells Kamisama what has happened with Gokuu, and that they are to wish him back to life using the Dragonballs only after a years (this gives Gokuu time to train in heaven).
Piccolo first part of training is survival. Gohan is placed in the middle of a forest for six months, and is to stay alive with no help from other people. During one of the nights, Gohan looks at the moon, and he turns into a were-monkey. Piccolo notices this and cut Gohan's tail off. Piccolo also gets a sword for Gohan, and a new uniform (it looks like Gokuu's old uniform except for the word "Ma" on it).
Bulma gets the power scanner working and checks out everyone sentou-ryoku. Kamesennin is 139, Kuririn is 206, Tenshinhan is 250 and Yamcha is 177. The group then goes in search for the Dragonballs.
After the six months were over, Piccolo started teaching Gohan attacking techniques and the use of magic. Gohan and Piccolo finally meet, and they talk. Gohan thinks that Piccolo is a nice guy, which just makes Piccolo angry.
Meanwhile Gokuu was still running on Snake Road. Gokuu eventually reaches the end of Snake Road, only to find nothing. Gokuu tells his Bo to extend, and catapults himself into the air. There is a sudden increase in gravity, and Gokuu finds himself outside of Kaiousama's house. Gokuu is greeted by Bubbles, Kaiousama's pet monkey. Gokuu tells Kaiousama that he wants to learn his special techniques, and Kaiousama accepts. Kaiousama wants Gokuu to attack, but the gravity is ten times stronger than normal, and Gokuu is having trouble moving. So instead, Gokuu is to try and catch Bubbles. Even without the weighted clothes, Gokuu is still too slow to catch the monkey. The first technique that Kaiousama teaches Gokuu is Kaiou-ken, which is a form of powering up. The next move is the Genki-Tama, which is a huge energy ball. However, because the fireball takes up so much energy, only one can be made. Kaiousama then tells Kamesennin to resurrect Gokuu.
Shenlong appears, and asks Oolong what the wish is. Oolong wants the Saiyan-jin's to disappear. Shenlong says that it can't be done (only certain can be made such as giving life etc.)So instead, Gokuu is brought back to life.
Piccolo realizes that the darkened sky means that the Saiyan-jin's are about to arrive, so he and Gohan leave from Kamesennin's house.
Nappa picks up two people with a power rating of 1000, so him and Vejiita go to investigate. Piccolo and Gohan meet up with Kuririn. The Saiyan-jin's then arrive and make fun of the three heroes. Nappa then reads their opponents power rating (Kuririn is 981, Piccolo is 1220, Gohan is 1083). Tenshinhan and Yamcha also arrive to meet the two Saiyan-jin's. Nappa creates six cybermen to fight the heroes (each cyberman has a power rating of 1200). Nappa can't believe it when Tenshinhan defeats his cyberman. Vejiita tells Nappa to stop believing in just pure numbers. Yamcha fights next, and defeats his cyberman. However, it comes back to life and self destructs, killing Yamcha in the process. Kuririn gets angry and blasts energy attacks at his opponent. However, he misses one, and the cyberman goes to attack Gohan. Piccolo easily destroys it with a swing of his arm. Gohan thanks Piccolo, and Piccolo says that he only done it as this was only the beginning of he fight. Vejiita and Nappa walk through the clouds of dust, without a single scratch on them. Nappa goes to attack the Heroes, and Chao-zu ESP doesn't work anymore. Nappa rips Tenshinhan's arm off, but is unable to finish him off. Nappa fires off an energy blast, only to create a missive hole in the earth. Piccolo is amazed by the power of Nappa. Chao-zu moves behind Nappa and self-destructs. However, Nappa survives the blast. Tenshinhan then does Kikouhou, causing Tenshinhan to die. However, this attack also has no effect on Nappa. Gohan prays for Gokuu to quickly arrive, and Vejiita wants them to stop fighting and wait for Gokuu. The two Saiyan-jins wait for three hours, and Gokuu doesn't appear, so they start attacking again.
Meanwhile, Gokuu has reached the end of Snake Road. Kamisama gives Gokuu two senzu seeds. Gokuu eats one of them, and becomes instantly recharged. Gokuu then calls for Kintoen, and heads for the two Saiyan-jins. Nappa gets attacked by Kuririn and Piccolo, only counter-attack and batter the guys away. Nappa then starts attacking Gohan. Kuririn gets angry and attacks Nappa. Vejiita likes Kuririn's attacks. Kuririn starts up Kien-Zan at Nappa, and fires them off. Vejiita tells Nappa to avoid the blast, which he does. However, the balls graze Nappa's cheek, causing them to bleed. Nappa gets fumed about seeing his own blood. Nappa then starts up a killing move, but Piccolo blasts him first. Vejiita then senses Gokuu's power approaching. Kakorat has a power level of 5000, and will arrive in four minutes. Nappa attacks Gohan, trying to kill him quickly. Instead, Piccolo saves his life by taking the damage. Piccolo tells Gohan that he is on his own, and dies. In heaven, Kamisama dies as well. Gohan uses Masen-kou and blasts at Nappa. However, Nappa just deflects the shot. Kuririn tells Gokuu about how everyone is dead, and Gokuu gives the last seed to Kuririn. Kuririn eats half of it, and gives the other half to Gohan. Gokuu powers up, and Vejiita gets angry when his scooter says that Gokuu is over 8000. Gokuu then starts beating up Nappa, and wins. Vejiita gets angry at Nappa, and kills him himself. Gokuu is trying to understand why Vejiita done this, while Gohan and Kuririn run back to Kamesennin's house.
Vejiita and Gokuu agree to move and fight in a better area (a place without living things). Vejiita tells Gokuu about the nature of a Saiyan-jin (being a fighter and conquering planets). Gokuu powers up, and then Vejiita does the same. Vejiita attacks, and Gokuu gets hit from behind. Gokuu then powers up to KK#3. They fight, and Vejiita gets angry at getting crossed up. Gokuu finally connects a punch, causing Vejiita to start bleeding. Vejiita gets angry, and starts up Gyarikku-hou. Gokuu responds with a Kamehame-ha. They both strain to overwhelm their opponent blast. Gokuu then enters KK#4, and pushes the blast into Vejiita. Vejiita frees himself from the rubble, claiming he is the strongest Saiyan-jin in the world.
Vejiita then creates an artificial moon, and turns into a were-monkey (Vejiita is able to control himself in the were-monkey mode). Gokuu then recharges up to KK#5. Vejiita hits Gokuu with a mouth blasts, and then brakes both Gokuu's legs. Gohan and Kuririn attack Vejiita in order to save Gokuu. However, Vejiita sees them and avoids their attacks. Yajirobee appears out of no-where, cuts off Vejiita's tail, and then runs away. Gokuu then gives the Genki-Tama to Kuririn, while Gohan distracts Vejiita. Kuririn shoots the energy ball at Vejiita, and hits him. However, Vejiita slowly gets up, and tries to destroy the whole area, only succeeding in blowing everyone around. Vejiita then sees Gohan's tail, and tries to kill the boy. Kuririn tells Gohan to look at the moon, which he does. Gohan transforms into a were-monkey, and Vejiita tries rip his tail off. Vejiita throws an energy ball which cuts off Gohan's tail, but is unable to avoid Gohan's partially changing body. Lying helplessly on the ground, Vejiita uses the last of his strength to summon his ship. Gokuu tells everyone to let Vejiita live as since he is going to leave, he shouldn't be hurt. The spaceship arrives, and Vejiita leaves, saying that it was fun.