The Cosmic Emperor is one of the five what-if saga in Dragon Ball Z: Budokai Tenkaichi. The protagonist of the saga is Frieza, and it revolves around him trying to defeat the Dragon Team and gain immortality by using the Namekian Dragon Balls. This saga is unlocked after beating the previous saga, "A Lonesome, Final Battle".
Frieza controls numerous worlds with his fearsome grip. With endless ambitions of destruction, he uses his minions to spread his evil throughout the universe. Upon learning about the existence of the Dragon Balls, Frieza travels to Namek, where he aims to wish himself eternally young.
First, Frieza confronts Vegeta, and manages to defeat him. Next, he confronts Goku, and defeats him also. Frieza confronts Krillin, who is afraid of his true power. He defeats him in a fight. Frieza confronts Goku, who is in his Super Saiyan form, and manages to defeat him with his Death Ball.
Afterward, Frieza confronts his brother, Cooler, and tells him that there is only one ruler of the universe and it is him. Cooler is angered that his brother can talk to him like that. Frieza defeats Cooler, who is amazed that his brother has gone soft on him. Frieza tells Cooler that his transformation is not powerful enough and is going to enjoy bossing him around for a change.
While Frieza managed to dispose of the Saiyans who kept him from his goal of eternal youth, his anger was turned on the rest of the universe, and he will surely make them feel his power. Still to this day, the cries of the dying innocent echo throughout the universe in vain.