WARNING: The following contains spoilers for Boruto: Naruto Next Generations Episode 218, "Partner," now streaming on Crunchyroll.
In the Boruto anime, fans are still stunned over how Isshiki Ōtsutsuki's reign finally comes to an end. Thanks to Kawaki's quick thinking, the alien has been killed, leaving the Konoha-nin scrambling to get back home. However, while the mission in a secret dimension is seen as a major success, the series manages to revive a despicable villain, leading to immediate repercussions.
After Isshiki crumbles to dust, Kawaki and Sasuke attend to the damaged Naruto in the wake of his Baryon Mode. The Hokage loses Kurama in the battle, but just as it seems like they are preparing for a solemn trip back home, Boruto flies in and stabs Sasuke in his Rinnegan eye.
It's a scene of stark terror, but it turns out this isn't Boruto; Momoshiki has taken over his body and fettered himself to the ninja's essence. The villain returns once more in full control, slaking his appetite for destruction after being initially killed by Boruto, Naruto and Sasuke. However, this time, he's used his own Karma mark to possess Boruto.
For some time, Momoshiki has been trying to make the spritely teen a perfect vessel, only to have the kid fight him off as a host. However, Sasuke realizes that while battling Isshiki, Boruto's chakra was expended, allowing Momoshiki to lay in wait. Once Isshiki was dusted, he piloted the boy's body and enacted this plan.
It's perfect timing, because Naruto is broken and severely de-powered with the Nine Tails Demon Fox dead, and with Sasuke's Rinnegan taken out, he can't teleport them across space and time again. In fact, the loss of his eye takes away several of Sasuke's most powerful techniques and removes the chances of him using the resurrection jutsu if he ever needed to. He and Naruto therefore become average ninjas once more, with Momoshiki playing the chessboard like a grandmaster.
Thankfully, Sasuke deduces that with enough chakra, they can fill Boruto's tank up again. It comes as he realizes that Momoshiki isn't absorbing his fire bombs, which means he doesn't want the extra chakra in him. Thus, Kawaki uses flames of his own, forcing Momoshiki to absorb them in order to block being incinerated. As he fills up, Boruto's levels rise once more and he takes back control, temporarily expelling Momoshiki.
Sadly, once his levels are depleted, Momoshiki will get to run the show again, so Boruto will need Katasuke and scientists from the Land of Fire to find a solution. The Hidden Leaf aren't experts on the Ōtsutsuki, however, so Boruto may require the shady ex-Kara scientist, Amado, to help out. Either way, they're all worried knowing that Momoshiki is lurking under the surface, eager to carry out the God Tree plan with the Ten Tails and obtain the chakra fruit that eluded both Isshiki and Kaguya.