You must be controlling Gohan and cannot have Vegeta in your party at all. You can find this substory during Intermission 2, with Oolong being found at Master Roshi’s house. He is curious as to why Gohan’s tail isn’t growing back and sends you to Kami, who was the one who took away Goku’s tail. Fast travel to Kami’s Lookout and upon speaking to him, you will learn nothing. Mr. Popo chimes in and says you should ask a Saiyan about this, with you being pointed in Vegeta’s direction.

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(1 of 2) Be mindful of the melee attacks Vegeta can do

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Be mindful of the melee attacks Vegeta can do (left), which can sometimes lead straight into a Galick Gun (right)

Vegeta can be found in the Central Plains Area of the world map, so head there and locate him. As soon as you speak with him, he asks you to fight him, so get ready to do battle. You should have a good idea what he can do, since you’ve played as him a few times now. If not, then he has a few melee attacks and sometimes will unleash a Galick Gun immediately after one of them, so be ready and a little defensive. He also has the one Super Attack where he shoots a bunch of Ki blasts at you. Upon winning the battle and asking Vegeta about the tail situation, you learn nothing concrete, but hypothesize something. You will automatically return to Oolong and finish off this substory.