The fate of Megumi Fushiguro in the current timeline of the Jujutsu Kaisen manga remains uncertain. This is mainly due to all the accumulated damage he had to endure due to all the atrocities committed by Sukuna, who is currently in possession of his body. Additionally, Sukuna transformed into his Heian Era body following his battle against Satoru Gojo, which left fans questioning if Megumi was even alive at this point.
Fortunately for fans, Megumi's survival was more or less confirmed in chapter 249 of the Jujutsu Kaisen manga, as Yuji Itadori's plan to save his friend was brought to light.
However, a recent fan theory seemed to suggest that even if Megumi somehow manages to survive, he may very well seal the fate of the world. This might happen if Megumi starts the merger between humanity and Tengen, similar to how Eren Yeager destroyed almost all of humanity in Attack on Titan.
Jujutsu Kaisen: Exploring the possibility of Megumi starting the merger and becoming the 'next Eren'
Before Kenjaku met his decisive end at the hands of Yuta Okkotsu in the Jujutsu Kaisen manga, he ensured the inheritance of his will by transferring the right to start the merger between Master Tengen and the humanity in Japan to Megumi Fushiguro. This meant that Sukuna, who is currently in possession of Megumi's body, technically had the right to begin the merger.
However, the latest chapter of the Jujutsu Kaisen manga seemingly turned the tide of the battle following the revelation of Yuta's Domain. It showed Yuji Itadori as he prepared to use his Soul-Swapping technique to rip Sukuna out from Megumi's body. While Yuta's Domain may have provided a faint ray of hope for the Jujutsu sorcerers, it still wasn't enough to guarantee their victory, since it's hard to imagine Sukuna losing to anyone at this point of the story.
That said, a recent fan theory on social media presented a What-If scenario. In the scenario, after the sorcerers eventually manage to defeat Sukuna and separate him from Megumi, the latter may end up starting the merger due to his broken state of mind. It would make him somewhat similar to Eren Yeager, who brought death upon 80 percent of humanity in his world, albeit due to different motivations.
For those unaware, in the world of Jujutsu Kaisen, the merger refers to the fusion of every human inside Japan with Tengen. This would likely spell the definitive end of the world, as it would effectively combine all humans into a single entity. The negative emotions from even one individual would quickly spread to everyone. In the end, it will result in an all-powerful malicious entity that could pose a greater threat to the world than even the King of Curses.
That said, for this theory to work, one should take into account all the pain and suffering Megumi had to endure while Sukuna was in possession of his body. Throughout the story, Megumi was trying to save his sister, Tsumiki Fushiguro, who was in a state of coma due to a mysterious curse.
However, Sukuna killed Tsumiki during the Culling Game arc, who was possessed by the ancient sorcerer Yorozu at the time. It was a deliberate part of his plan of completely breaking Megumi's soul, so that he would no longer be able to fight back against him.
Afterward, Sukuna also utilized Megumi's soul to survive attacks from Satoru Gojo's Unlimited Void Domain. He even killed the latter by using the abilities of Megumi's strongest Shikigami, the Divine General Mahoraga. The fact that Sukuna killed two of the people closest to Megumi, while possessing his body might be enough to completely shatter his soul and deprive him of his will to fight even if he gets rescued.
As such, the theory suggested that Megumi might undoubtedly be in an unstable state of mind if he gets freed from Sukuna. He might start the merger between Tengen and all the people in Japan out of pure anger and hatred for everyone.
Considering that Yuji felt responsible for all the people that Sukuna had massacred in Shibuya, it would be safe to assume that Megumi would be no different. Being the one who ended the lives of his teacher, who saved him from the Zenin clan and gave him a home, and his sister, who was his only reason to fight, Megumi would feel devoid of any purpose and might bring an end to all of humanity.
This would also resonate with the time when he once told Yuji that it's never guaranteed that someone he once saved would not kill someone else in the future. Even though Yuji and the rest of the sorcerers give it their all in defeating Sukuna and saving Megumi, the latter may not be the same person he was before.
Due to everything he has endured so far, coupled with his fractured state of mind, Megumi might end up becoming the bane of humanity and destroy everything he once sought to protect.
Final Thoughts
At the end of the day, however, it is simply a theory that would without a doubt, completely alter the course of the Jujutsu Kaisen series. A character straying away from their morals after suffering unfathomable losses isn't entirely uncommon in the anime industry.
However, it would definitely be the most shocking yet heartbreaking moment of the entire Jujutsu Kaisen manga if Megumi decided to destroy the world after his allies gave it their all to save him from The King of Curses.