Attending a reunion at Master Roshi's house, Goku notices an incredible power approaching the house. Though Goku does not know it, he is about to meet his brother Raditz. The encounter with this powerful alien, who like Goku belongs to a race known as the Saiyans, is only the beginning of this story.
Teaming up with Piccolo, Goku is able to defeat his brother only at the cost of his own life. Before being destroyed, Raditz reveals Goku's origins and that he was originally sent to Earth to destroy it. The evil alien has the final laugh as he explains that two other Saiyans, more powerful than he, are already on their way to finish the job. The defenders of Earth have only one year to prepare, as well as wish Goku back to life with the Dragon Balls.

In the Next Dimension, Goku spends the better part of the year trying to get to King Kai's house to get the training he'll need. The journey is long and treacherous, but eventually he makes it. Meanwhile, the Z Fighters go all out in their training and preparation under Kami's tutelage. Piccolo takes Gohan, Goku's son, under his wing and begins to turn the little boy into a powerful young fighter. Though he tends to be hard on the boy, the two do forge a very strong friendship.