WARNING: The following contains spoilers for Boruto: Naruto Next Generations Chapter #54, “Bro,” by Masashi Kishimoto, Mikio Ikemoto, Mari Morimoto and Snir Aharon, now available in English from Viz Media.
Since Chapter #53, the Boruto manga has painted an even more ominous picture for Sasuke, Naruto and Kawaki now that Momoshiki has successfully taken over Boruto's body. Right after they were able to defeat Isshiki, the other Ōtsutsuki clan-member saw an opening for possession after the teen's chakra levels dropped, as he now had another window of opportunity to conquer Earth.
However, in Chapter #54, Kawaki makes a sacrificial move that almost costs him his life and in the process, revives Boruto so they can figure out a way to expunge the alien from his body.
Momoshiki's been quite a handful -- nullifying the team's efforts by stabbing Sasuke in his Rinnegan eye. Meanwhile, with the current Hokage drained and unconscious, the Uchiha Ranger depowered and Kawaki not as strong after Isshiki tried to possess him, Momoshiki thinks it'll be a walk in the park to finish what his brethren started. But thanks to Sasuke's genius in Chapter #54, Kawaki is able to come up with a Hail Mary play to save the day.
Sasuke discovers that after attacking with his sword and lightning that somehow Momoshiki isn't absorbing jutsus with his Karma mark. It's usually Momoshiki's go-to move, which Sasuke tests even more by using his flame techniques. When he sees Momoshiki using a shadow clone to literally take the heat, he confers with Kawaki on a hunch. He's confident Momoshiki can't absorb the moves because once he absorbs the natural chakra embedded within them, it'll raise the vessel's overall chakra reservoir and activate Boruto's consciousness again.
In other words, feeding Momoshiki chakra will reawaken Boruto. The alien realizes they're coming up with tactics against him so he speeds up his plan to go after Kawaki by taking Sasuke out. However, Kawaki is pretty intuitive, and right when Momoshiki comes for him, Kawaki uses a flame technique of his own to set his body on fire. Momoshiki's shocked as he can't believe he pulled this suicidal move, but it's a win-win for Kawaki.
Clearly, Kawaki would prefer to die than let Momoshiki take him for the God Tree, while the other option would bring success as well. The latter is the route Momoshiki goes down as he has no choice but to absorb the flames to protect Kawaki's body.
The fact is, he needs him as an offering but as planned, this high-level of chakra (Kawaki has Isshiki's Ōtsutsuki DNA in him) that he sucks in allows Boruto's mind to power-up and take control of his body again. As he sends Momoshiki to his resting place, Boruto thanks a badly burnt and beaten Kawaki. However, it's only a temporary victory as they now have to extract Momoshiki's presence for good or risk another dangerous episode in which he comes out hungry for death and destruction again in the Boruto manga.