Super Saiyan God-Blue is a technique invented by Vegeta in the manga and Goku in the anime, in which they rapidly switch between the Super Saiyan God and Super Saiyan Blue forms in order to utilize Super Saiyan Blue's power to its full potential. In the anime Whis explains that Super Saiyan God is faster than Super Saiyan and uses far less stamina so by only using Super Saiyan Blue for brief moments while attacking, one can maximize power and speed while using almost no stamina.
Despite Super Saiyan Blue having vast strength, it has a weakness in that it consumes energy at such a rapid pace that the user cannot maintain the form for too long. To overcome this weakness, Vegeta went through extensive training in order to obtain a technique that allows him to use the form's full power without losing strength.
With this technique the user stays in Super Saiyan God form and only in the instant that they attack or defend, transforms into Super Saiyan Blue. It is done with such speed that their adversary barely notices the transformation happen. By doing this the user is able to store the power of Super Saiyan Blue and then let it explode when needed.
In the manga, Vegeta uses this technique in his second battle with Goku Black, managing to overwhelm him despite his usage of the Super Saiyan Rosé form. Prior to this Goku briefly uses a similar technique against Hit in the Tournament of Destroyers, however he was only able to make the switch once whereas Vegeta was able to do so repeatedly.
In the anime, during the Tournament of Power, it was Goku who came up with the strategy instead of Vegeta, and uses this technique to combat Dyspo and Kunshi and with Hit's help, puts them on the firm defensive with Goku using this to read and counter Dyspo's speed. Whis explains that Super Saiyan God is Goku's second fastest form and uses far less stamina than Super Saiyan Blue and only using Blue for a moment to attack therefore maximizing his speed and power. Beerus is actually highly impressed by the technique, who proudly exclaims "That's our Goku" after seeing Goku perform the technique to great effect.
- This technique is very similar in usage to Goku's early use of the Kaio-ken, activating a state of much higher power for a fraction of a second to overwhelm an opponent or increase speed.