Obtained: Speak with Cui as Vegeta near Gizard Wasteland in the Central Plains Area during Main Story Intermission 3
Objective: Defeat all enemies
In order to fight Cui, you will need to revive him using the Dragon Balls. Afterwards, travel to the Gizard Wasteland in the Central Plains Area to find him. Speak with Cui to fight and defeat him to complete the story.