After Son Goku taught the five of them how to cultivate divine power, they began training in earnest.
After spending two years in the Hyperbolic Time Chamber, all five successfully reached the Super Saiyan God realm.
Unlike becoming a Super Saiyan God through an infusion of heart energy, reaching that realm through their own training elevated their level of existence, bringing their lifespans on par with a Supreme Kai's.
This was also why Son Goku had taught the five to cultivate divine power. Although Super Saiyan 4 and higher forms also elevated one's level of existence, their lifespans still fell within mortal limits.
After coming out, the five rested for two days before resuming their training.
Inside the Hyperbolic Time Chamber, Son Goku hit a bottleneck. Although his strength continued to rise steadily, he had no idea how to achieve Super Saiyan 8.
So Son Goku simply set aside his attempts to uncover Super Saiyan 8 for the time being and turned to training his divine power, God of Destruction Technique, and Ultra Instinct.
Bang! Son Goku transformed into Super Saiyan Blue Evolved, then tried stacking Super Saiyan 3 on top of it.
"Aah! Aah! Aah! Aah! Aah!"
As he roared as though straining with constipation, Son Goku's blue hair rapidly lengthened, his brow ridge gradually protruded, and his eyebrows slowly vanished. Deep blue flames rose around him like burning firewood.
Noticing these changes, Son Goku sped up the stacking process.
A moment later, Son Goku stood there in a form that combined Super Saiyan Blue with Super Saiyan 3.
Blue flames wreathed his body, threaded with dense white lightning. At that moment, Son Goku looked almost identical to his Super Saiyan 3 form, apart from his hair and the flames surrounding him.
Son Goku looked himself over, then raised