After killing Cell, Trunks returned to the Space-Time Secret Realm to continue training.
Scumbag Kakarot went in once every few hours.
Ten days passed like this before this timeline's Son Goku, Vegeta, Piccolo, Trunks, Son Gohan, and the others emerged from their training.
After nearly three hundred years of training in the Space-Time Secret Realm, Vegeta and Son Goku had reached Super Saiyan 7. Son Gohan and Trunks had only just broken through to Super Saiyan 7, while Piccolo had attained his diamond form. To advance any further, he would have to fuse with old Kami.
But having reached this level of strength, Piccolo no longer considered fusing with old Kami worth his while.
After their happy reunion, it was time to part again. As everyone watched, Scumbag Kakarot set off on another journey through time with Chi-Chi, Bulma, and Lazuli. Piccolo 3 tore open space-time himself and returned to Universe 3.
Many years later, when Buu, Janemba, Beerus, Golden Frieza, Fused Zamasu, and Black Frieza encountered Son Goku, Vegeta, and the others, every last one of them was left dumbfounded as Son Goku, Vegeta, Son Gohan, and Trunks took turns beating them senseless.
Beerus lasted fewer than two moves against Vegeta before Vegeta knocked him unconscious.
"So this is a God of Destruction? Not much to speak of," Vegeta said disdainfully.
When Beerus woke up, he was furious. After stuffing himself with food on Earth, he reflected bitterly on his defeat and decided to train for twenty years straight.
Twenty years later, Beerus had perfected both his great techniques, Ultra Instinct and Ultra Ego. He faced Vegeta again and defeated him in two moves, avenging his own two-move defeat twenty years earlier.
After defeating Vegeta, Beerus resumed his lofty, superior air.
"This palm strike carries twenty years of training.