The deuteragonist of the Naruto series, Sasuke Uchiha is one of the most powerful characters Boruto era too. He stands tall as the second Hokage of Konoha, supporting Naruto Uzumaki from the shadows and protecting the village from threats that even Naruto cannot see. Sasuke is an incredibly powerful ninja, widely regarded as the strongest in the world next to Naruto Uzumaki. As such, he has quite a few powerful abilities up his sleeve, some of which can cause catastrophic damage.
Until recently, Sasuke had access to his Rinnegan, giving him a wide variety of techniques to use in battle. Now that he has lost this power, his strongest jutsu arsenal has changed dramatically. IN Boruto: Two Blue VortexesSasuke's most powerful jutsu is a unique technique that can deal devastating damage to his enemies even though he no longer has the Rinnegan. This jutsu is a Kagutsuchi Chidori that he can still use, especially in conjunction with his full body Susanoo, making it one of the most powerful techniques that exist in the world. Boruto.
Sasuke Uchiha losing his Rinnegan means the full body Susanoo Kagutsuchi Chidori is his strongest Jutsu
Sasuke Uchiha awakened the power of the Rinnegan in Naruto Chapter 674, which was published in Shueisha's Weekly Shonen Jump Issue #22-23 on May 12, 2014. It was in this chapter that Sasuke received half of the Sage's power and as such gained access to the R Sixinnegan. With it, he could do things like manipulate gravity, absorb chakra, use various summons, and gain absolute control over life and death, among other things.
In the Boruto series, Sasuke was extremely nervous because his Rinnegan was not used properly. Even so, he has now completely lost his Rinnegan, meaning that his true strongest abilities are no longer available to him. As for his current strongest Jutsu, Sasuke has the Kagutsuchi Chidoriwhich he used for the very first time in Naruto Chapter 698 on November 17, 2014 in Shueisha's Weekly Shonen Jump #49. To perform this technique, Sasuke combined the power of his Blaze Release: Kagutsuchi with the Lightning Release Chidori. The combined use of these powers drastically increased his offensive power and ensured that his Chidori was strong enough to break through even a Rasengan enhanced by six paths. This jutsu was so powerful that it completely blew off Naruto's arm and caused devastating damage to Sasuke himself.
“So here's the thing. I'll use the Kagutsuchi with the Chidori and take it out in one attack.” — Sasuke before using the Kagutsuchi Chidori, Naruto chapter #698
Now as an adult, Sasuke has better control over not only this jutsu, but also his other Mangekyo abilities such as Susanoo. As such, it should be possible for him to combine Full Body Susanoo and Kagutsuchi Chidori, which could give rise to his new strongest jutsu after 12 years.

Boruto officially establishes his greatest romantic couple at the end of the game
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Why is Sasuke's new strongest Jutsu still strong enough to defeat Otsutsuki level ninjas
Kagutsuchi Chidori is one of the most underrated jutsu in the Naruto universe. This technique, despite having little chakra, was capable of causing six-path level damage to individuals at the time. However, since then, Sasuke Uchiha has grown tremendously in terms of strength. His control over nature transformations has improved dramatically and his use of the Mangekyo Sharingan is much better than ever before. Putting two and two together, Sasuke's Kagutsuchi Chidori is much better than ever right now, and what's more, he can now combine this jutsu with his Susanoo as well. There is absolutely no reason to believe that Sasuke can't do this, given that he has already shown the use of the Susanoo Chidori in Chapter 695 of Naruto.
“Forgive me Boruto. Stopping Momoshiki's rampage was my responsibility as your teacher, but I couldn't be there for you when you needed me. The village doesn't need to hate anyone but me.” — Sasuke Uchiha prepares for new challenges, Boruto: Naruto Next Generations Chapter #69
By combining Kagutsuchi with him, Sasuke can create a devastating technique that should theoretically be able to take down even Otsutsuki-level ninjas. The only problem is that the Otsutsuki are strong enough to absorb any ninjutsu based abilities. This is exactly why this technique has to be launched at the last moment before they are absorbed, and if they hit, they can easily take down the Otsutsuki in one hit. This is especially true when you look at Sasuke's overall power level in Boruto: Two Blue Vortex. After the three-year timeskip, Sasuke is much stronger than he was before, although he officially lost his Rinnegan in Boruto: Naruto Next Generations Chapter 53 on December 20, 2020, losing his greatest asset.
Sasuke has trained his mind and body in such a way that he is much stronger than before. In his battle against the Code, introduced in Boruto: Two Blue Vortex Chapter 5 on December 20, 2023, Sasuke was seen to be strong enough to tear out one of his eyes. The code is stronger than the Jigen that Sasuke fought against in the battle despite having the Rinnegan in Boruto: Naruto Next Generations Chapter 38. It is clear that he is on a completely different level of power right now. His control over unique powers like Kagutsuchi Chidori as well as Susanoo will be on a whole other level.
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Code: Uchiha, you!!! How dare you take my eye?
Sasuke: Listen carefully, Boruto! We can't win against him now. So run away. Survive at all costs and build on the skills I have drilled into you. Then no one will be able to stop you.
— An exchange between Sasuke and Koda showing the former getting stronger, Boruto: Two Blue Vortexes Chapter #5
Sasuke Uchiha has more big upgrades lined up in Boruto: Two Blue Vortex
Boruto: Two Blue Vortex prepared an even more significant upgrade for Sasuke Uchiha. The very first of these upgrades was teased in Boruto Volume and reiterated in Boruto: Two Blue Vortex Volume #8, where it was stated that Sasuke Uchiha trained his mind and body together with Boruto Uzumaki. Later it was also confirmed in Boruto: Two Blue Vortexes Chapter 28 that Sasuke's sword has been upgraded by Sumire and his chakra has been registered, meaning that this new, sharper, stronger and better blade can be wielded by the Uchiha, which also increases his overall power.
“The hilt has been reworked from the original material to a form that maximizes its strength. That's not all, your Uchiha-style Hagoromo Kenjutsu will sustain itself once you grasp the hilt.” — Sumire explains Sasuke's sword upgrade, Two Blue Vortexes, Chapter #28
Additionally, Sasuke will likely gain a significant buff to his base form when he no longer has the Rinnegan. Right after Sasuke returns, probably at the end of the Hidari arc that already started in the Two Blue Vortex manga, Sasuke will likely be seen reaching a whole new level of power. We absolutely can't wait for Mikio Ikemoto and Masashi Kishimoto to show it off. Perhaps in his upcoming battles in the Boruto series, he is about to unleash the power of his Susanoo: Kagutsuchi Chidori and show fans why even though he is past his prime, he is still among the strongest in the world.
The latest chapters of Boruto: Two Blue Vortex by Mikio Ikemoto and Masashi Kishimoto are available to read via Manga Plus and Viz Media.