Goku Black explains that he is Zamasu from an alternate timeline where he succeeded in killing Gowasu, the Time-Ring allowing him to be unaffected by his past self's death. The other Zamasu then formally introduces himself as the Zamasu of Future Trunks' timeline, whom Black allied himself with as they destroyed the Super Dragon Balls after using them to grant Zamasu indestructibility. They then killed the other deities so they would not interfere in their goal of wiping all mortal life for their ideal utopia, saving Earth for last to have the humans suffer an agonizing demise. In the battle that follows, Zamasu and Black provoke Goku into giving the latter a challenge after revealing that Black also killed Chi-Chi and Goten when he acquired his new body and killed the alternate Goku. The two manage to defeat Goku before turning their attention to Future Trunks and Vegeta, both telling the former that his constant meddling in the timeline is the reason for Earth's misfortune. This infuriates Future Trunks, who explodes and transforms into an immensely powerful new Super Saiyan form.

After being saved by the resistance, Future Trunks comes to and learns of Future Mai has found the villains' hideout and saves her after her failed attempt to snipe Goku Black. Future Trunks fights the two again and fails after attempting a suicide attack to destroy Zamasu's body, Goku and Vegeta arriving just in time to save him. Goku Black damages the Time Machine to prevent them from escaping again as Gowasu appears with Shin in an attempt to reason with his apprentice. But Black and Zamasu reveal their actions of slaughtering the other deities, with Goku learning that a Destroyer's death means their angel attendant like Whis enters an inactive state until a replacement appears. Zamasu and Black attempt to kill Gowasu before Goku and Vegeta intervene and battle them while Bulma begins repairing the Time Machine and having Future Trunks repair the sealing urn which Goku brought. Vegeta gets the upper hand over Black due to his training, denouncing his opponent as a thief who never worked to gain his power like any real Saiyan would.