Goku and Vegeta's training with Whis and Beerus is interrupted by the arrival of Future Mai, who tells them that Future Trunks has been captured. A mysterious figure emerges, introducing himself as Fu; he tells Goku, Vegeta and Mai that Future Trunks is trapped on a world called the "Prison Planet", a planet where warriors from alternate timelines and dimensions fight as part of an experiment conducted by Fu. The trio arrive on the planet and meet an alternate version of Goku called "Xeno Goku", who transforms into Super Saiyan 4 and attacks Goku, who reacts by transforming into Super Saiyan Blue. During the fight, Goku discovers that there is an invisible barrier around the Prison Planet that prevents them from escaping. Then Fu disappears, and the two Goku agree to work with each other to escape the planet. In the end, Fu observes the Prison Planet and tells a seemingly evil Saiyan that his time will come.

Goku and company are helpless against the evil Saiyan who is shrouded in an overwhelming large, sinister ki! Goku is enveloped by the evil Saiyan’s ki and runs wild, but an unexpected savior comes to the rescue!

The evil Saiyan Cumber has now revealed his true form, and in order to face off against him, Goku and Vegeta fuse via the Potara! They become the mightiest warrior, Vegito Blue, and even let loose with the Kaio-Ken!! Cumber counters by unleashing an amazing form.

Cumber unleashes his fearsome form and runs wild. His power is too much for the Prison Planet to handle, and the chains start to snap one by one. Seeing this throws Fu into a rage, and he unleashes his hidden power.

As Goku and company are in a jam, Xeno Goku and Xeno Vegeta come to their aid, having noticed the change in the Prison Planet. To counter Cumber's bottomless power, the two use the Potara to fuse! It's the explosive birth of the mightiest warrior!