Dragon Ball cenitures arc
After the son of brolly achieve super sayan rosa.
Gkou comes up to Goku Jr, and offers to take him to the dragon world to teach him how to fight
Goku: hey Goku jr: Its you Gokul Yeah I am your great great, how many greats again grandfather Goku; It looks like i left you with a bit of a mess Goku; I would like to help you protect earth so things like pan dying doesn't happen again Goku Jr; I would be honored to train with my lengenday great great, well my grand father
Goku: great lets get to work, where we are going anything is possible Goku; Right now you are immortal so dont be afraid of dying the fight just go all out with me and it will train you 1000x times faster than any training you would get from piccolo on earth Goku: Make us immortal sheron Sheron: so be it
So goku and Goku jr proceed to train with one another. Goku Jr eventually prefects super sayan blue.
Goku: I m proud of you grand son, you did something that took me years to prefect in only a week, now that's talent Hehe
Goku Jr: well gosh thanks, I thought you where good but you showed me what power was
Goku; You are strong enough to beat brolly son now Goku; Go give it to him
Goku Jr goes and fights pargous and wins the battle.