WARNING: The following contains spoilers for Chapter #54, “Bro,” of Boruto: Naruto Next Generations by Masashi Kishimoto, Mikio Ikemoto, Mari Morimoto and Snir Aharon, now available in English from Viz Media.
In the final chapters of Naruto, the title character and Sasuke had a battle for the ages. They fought and destroyed the monuments to Hashirama Senju and Madara Uchiha, giving the impression there would never be peace between them based on Konoha's dirty past and what it did to Sasuke's clan.
Despite beating Kaguya, they couldn't settle their differing philosophies on world peace and it culminated with Naruto maxing out his Rasengan and Sasuke his Chidori. The impact of these nuclear blows then caused both of them to lose limbs and fall. Luckily, as they lay beside each other, they finally buried the hatchet with Sasuke accepting Naruto as a brother. Boruto #54 recreates this iconic moment between Boruto and Kawaki, with a slight tweak.
When Naruto and Sasuke had their moment, the entire Valley of the End was destroyed due to their rage. They were bleeding, frustrated it got this far, which led to them falling asleep next to each other and waking up the next day. Sasuke admitted defeat but Naruto was annoyed, feeling they needed to rest and have one last fight in the future. As is their dynamic, they called each other names, but Naruto admitted he always felt Sasuke's pain, which is why he never gave up or tried to kill him. No matter what, they were like siblings, which resonated and changed Sasuke forever.
Something similar happens in the aftermath of the Momoshiki battle as Kawaki and Sasuke struggle to defeat the alien, who has fully possessed Boruto. Luckily, Kawaki tricks him into absorbing flames, which raises the chakra level and allows Boruto to take control of his body again. Exhausted from the fight, Kawaki drops to the ground after using up so much chakra. Boruto falls down next to him, saying sorry for the trouble he caused, but as they shoot each other sly grins, Kawaki tells him he's sorry for the trouble he caused too, calling Boruto his "stupid bro."
This is them finally accepting each other as brothers, so symbolically it's a carbon copy of Naruto and Sasuke's epiphany. Kawaki, no longer bitter, has lost his right prosthetic arm, which is the same hand Naruto lost so there is collateral damage. Ironically, the Hokage gave him this hand as Kawaki lost his real one on the run from Isshiki and Kara, which annoyed Boruto weeks ago. However, there's no more bad blood because Kawaki went to the extreme for him, as Naruto did for Sasuke.
Thankfully, Boruto still has his right hand, although he has to figure out what to do about his Karma mark as it's a gateway for another possession. They're lucky they're not bleeding out like their predecessors, but seeing them passing out next to each other, expressing love in their own macho way, is a nostalgic callback. Sadly, it isn't a happy ending. They're still destined to fight each other when they're older, with Kawaki having killed Naruto and decimated the Hokage mountain.