This is the first in a series of blog short stories showing where I think a DBZ Character's limits are...
Sometime after the events of the tournament held in Universe 6, Vegeta is training on a remote desert planet. Wearing the armor given to him by Bulma, which has Whis' symbol on it, he trains in his base form.
He has worked up a sweat after training so long. After resting for a while, he clenches his fists and shouts.
"I WILL NOT LET KAKAROT SURPASS ME! NEVER!"
He had thought that he and Goku were equals, but, he had an ability that he did not. The Kaio Ken. He wanted to find a way to surpass Goku--without even attaining the Kaio Ken.
Vegeta powers up into a Super Saiyan and screams at the top of his lungs, producing a flashing gold aura and a shockwave. The ground trembles and cracks form, as the planet feels the force of a portion of his Saiyan power.
He powers up further---his aura turning into a blue one. His hair and eye color change from gold to blue, as he is transformed into his Super Saiyan Blue State, controlling god ki.
Testing the limits of Super Saiyan Blue, he begins to power up even more. His blue aura flashes brighter as his power begins to reach higher levels.
Meanwhile, on Planet Beerus, Whis is sitting down eating some alien food while Beerus is sleeping. Goku is not present as he is currently on Earth, recovering from using so much ki against Hit.
Whis sees Vegeta in the sphere on his staff, noticing that he is training. "Well, well, looks like Vegeta is testing his limits. I'd like to see where this goes."
Vegeta was controlling his ki as to not destroy the planet he was on, but was reaching higher levels. The power of himself as a Super Saiyan Blue had tripled, but he could not ascend further. He was beginning to tire out. Reverting to his base form, he panted.
"Well, it looks like I am nearly as strong as Kakarot's Kaio Ken times four...not good enough. Eh, at least his Kaio Ken times ten could only be used for a brief moment."
Suddenly, he had an idea. Vegeta powered up into a Super Saiyan once again, then ascended into a Super Saiyan 2. He looked the same as he did in his first Super Saiyan form but with lightning surges through his aura and was slightly bulkier.
"I need to master this...so that I can become...a Blue Super Saiyan 2!"
He began to power up, attempting to use god ki to multiply his Super Saiyan 2 power. He had not been able to achieve Blue Super Saiyan 2, but neither had Goku. They still needed to master the forms using their power as Saiyan beyond gods.
Attempting to mix god ki with Super Saiyan 2, Vegeta's aura had a blue ish tint and his power had slightly increased. He had only partially transformed and needed more training to become a Blue Super Saiyan 2.
"No...I cannot become one just yet."