The final series of Dragonball Z starts off with Gokou competing in a fighting tournament in one of the four Kaiou's planet. The result is that Gokou ties with his worthy opponent. Meanwhile, Gohan is training Goten in martial arts while Vegeta trains Trunks. Both Gohan and Vegeta are surprised at how strong Goten and Trunks are as they turn into their Super Saiyan form at such a young age. Gohan also has a girlfriend (Sataan's daughter).

Later, Gohan, a hero who has achieved the identity as the Great Saiyan-Man, attends a tournament. When it is the Great Saiyan-Man's turn to compete, he turns into his Super Saiyan form and his disguise is blown off. Everyone is amazed that a nerd, Gohan, is the Great Saiyan-Man. All of a sudden, Spopobitch and Yamu come out of nowhere and absorb Gohan's energy into a "lamp" to revive Boo. Kaiou-shin and his partner, trying to prevent Babi-di's and Darbura's plot to reactivate Boo, allow this to happen so that he could follow the energy stealers to their hideout. (Babi-di's goal is to destroy all life just for the fun of it.) But, he revives Gohan first. The Saiyan warriors decide to go as well. A fight follows. Darbura turns Klilyn and Piccolo into stone and Kaiou-shin's partner is killed. The Z warriors learn that Klilyn and Piccolo will return to normal once Darbura dies. In battle, Vegeta is turned into Babi-di's slave (this is when the "M" appears on Vegeta's forehead). His energy is used to reactivate Boo. Boo betrays Drabura and eats him. Thus, Piccolo and Klilyn are returned to normal. Majin-Vegeta beats Gokou, and then goes to fight Boo. Upon failing, Vegeta self-destructs and dies. Afterwards, Bulma gathers the dragonballs to revive all those killed since the fighting tournament. In the fights later on, Gokou gets angry enough and reaches Super Saiyan form 3 for the first time! (In stage three, Gokou has long hair and is more powerful than ever.) Gohan also heads to Kaiou-shin's planet, pulls out the Z sword, and trains under Dai Kaiou-shin. Goten and Trunks train as well to get stronger. From Gokou, they learn the art of fusion to fuse to become one, becoming Gotenks!

However, our heroes are still no match for Boo. Although Darbura's, the Prince of Darkness (Babi-di's associate who looks like a devil), and Babi-di's (a little ugly sorcerer with tiny hairs growing out of his body) other minions are killed, Boo gets stronger. Boo later revolts against his master (Babi-di) and kills him. Before their deaths, the villianous Babi-di and Darbura have casted a spell that turned Vegeta evil. However, in addition with fighting against Gokou, the evil Vegeta also fought Boo. Althought defeated by Boo, Vegeta later turns good again. It is here that Vegeta finally officially becomes one of the good guys. (In previous times, Vegeta only aids our heroes to assure that Gokou lives long enough for him to kill him. But, he never attempted to kill Gokou since the early battle against him in the Vegeta Series. Next, Boo separates into two forms-one good and the other evil. Evil Boo defeats good Boo, turns the him into a cookie, and eats him. From this method, the evil Boo gains the good Boo's powers and changes into a stronger form. Boo, previously fat, is now skinnier and taller, not to mention a lot stronger. Gotenks is also stronger; he is now able to turn into Super Saiyan stage 3, like Gokou. But, he is still defeated on one of his encounters with Boo and Boo engulfs SSJ3 Gotenks. Thus, Boo absorbed Gotenks' powers and becomes stronger again. He changes form again! (His "antennae" grows longer and he now wears a black vest like Gotenks'.) Piccolo is also defeated and eaten by Boo. Meanwhile, Gohan had mastered the Z sword and learned how to use his hidden powers without getting angry under training with Dai Kaiou-shin. (He does not turn into his Super Saiyan form for the rest of the series at this point.) Unfortunately, he too is defeated and engulfed. Boo, now with Gohan's powers, changes form again. (He now looks like he's wearing Gohan's clothes.) With the other warriors defeated, only Gokou and Vegeta are left to battle against Boo!

Gokou is still dead and watches the fight through Kaiou-shin's crystal ball. Seeing the unfortunate odds for our heroes, Dai Kaiou-shin sacrifices he life to Gokou and dies. Gokou's halo disappears, and Dai Kaiou-shin wakes back up with a halo over his head. Now, Gokou teleports into the battle. Vegeta, still dead, is also sent into battle by the judge of death. (Thus, Vegeta also comes back to life.) Gokou acquired a pair of special earrings from the Kaiou-shins that when each one is worn by different people, the two will permanently fuse. With Gokou wearing one of the earrings and Vegeta wearing the other, the two are pulled together and fused into Vegetto! At Vegetto's turn to fight Boo, Boo seems to be of no match to Vegetto, but Vegetto purposely gets eaten by Boo to save the other Z warriors. This cancelled the effects of the permanent fusion in Vegetto and Vegetto fisses back into Gokou and Vegeta.

Next, Boo undergoes another form change and temporarily becomes very muscular as he stands still in pain through the form change. Gokou and Vegeta are now inside of Boo's organs. They find Trunks, Goten, Gohan, and Piccolo, and rescue them by carrying them out of one of Boo's pores. As they leave Boo, the warriors grow bigger and are restored to their normal size. Fat Boo, the good Boo, also escapes from Boo's body. The evil Boo, still "puffy" and bulky, is undergoing his form change to restore to his original form. (The Kaiou-shins cursed him into his previous fat looking form for destroying their people.) Afterwards, he is little and short. Next, evil Boo does a giant fireball and blows up Earth!!! Luckily, Gokou had enough time and teleported himself and his comrades to another planet. Later, the Namek dragonballs are gathered and a wish is made to restore the earth. The little Boo also met with the fat Boo. They fight, but the good Boo is once again defeated.

I don't know how and why, but Gokou and Vegeta are later alone somewhere fighting Boo. Vegeta stalls Boo as Gokou gathers the energy to do a super Genki-Dama fireball. While Vegeta is getting kicked around by Boo, Piccolo, Gohan, Goten, and Trunks are on earth trying to convince the earthlings to raise their hands so that their energy will be given to aid Gokou strenthen his fireball. Because no one on earth listens to the heroes, a new approach is taken. Sataan is contacted for help. Because of his fame, he goes into public and raises his hands. All of his fans, everyone on Earth, raise their hands too to show their appreciation to Sataan. With everyone's hand raised, energy is transfered to Gokou and now has enough power to destroy Boo. With a single super fireball, Boo is destroyed.

At the end, the fat Boo, who was beaten unconscious, awakens and enters our heroes' side. Ten years past. Goten and Trunks are now teenagers. Gohan married Videl and now has a 5 year old daughter, Pan. Gokou wished to fight the evil Boo all over again, so he wished for the reincarnation of the evil Boo. The evil Boo, now Ubuu, is reincarnated (and not evil anymore) and under the training of Gokou. There is peace on earth..