Boruto: Two Blue Vortex continues with the next step in the fight against the Shinju (God Trees).
The latest chapter of the series has explained how Uzumaki Boruto was able to become so powerful so quickly after the time jump. Boruto: Naruto Next Generations ended with Boruto being forced to escape from the Hidden Leaf Village, as he decided to train as much as possible, preparing for his final rematch with Kawaki and Code. The new manga Boruto: Two Blue Vortex picks up three years later, and Boruto has been revealed to have a number of powerful new skills, which he was able to learn in a short period of time.
Cover of Boruto: Two Blue Vortex chap 13
Boruto: Two Blue Vortex is slowly revealing more of Boruto's new techniques and also explaining why he can use them without the help of Uchiha Sasuke.
Although Sasuke offered to help Boruto during the chaos at the end of Boruto: Naruto Next Generations, the latest chapter of Boruto: Two Blue Vortex revealed that Boruto was able to learn powerful new attacks thanks to the surprising help of Kashin Koji, who was able to see multiple futures in which Boruto learned those techniques.
This information helps fill in some of the gaps in the time skip, as it is revealed that after Sasuke was captured and turned into a tree, Boruto himself was left without any potential help. At this point, Kashin contacted Naruto's son and explained that he had unlocked a new Shinjutsu, Prescience. This new ability allows Kashin to see multiple futures. Whether Boruto doesn't believe Kashin has that power, or even trust him, the man still offers to help, so they can avoid the worst possible futures.
While Kashin's ability does not confirm whether the future will happen or not, as it is always changing, it will provide them with valuable information on how best to change the future. Kashin then explains that he will reveal the future techniques that Boruto will master in the coming years, which will speed up his training.
That's why Boruto became so powerful, with things like the new Rasengan technique and more. Because he can basically learn from his future self's mastery of that technique. Now, it's just a matter of seeing how it can change the future.
