Yuji Itadori could still be the main character. He might have developed new and more powerful techniques in this fanfiction, and be the one leading the charge against new threats in the future of the Jujutsu world.
Maybe in the fanfiction, the story focuses on a character from the future coming back to the present in 'Jujutsu Kaisen Watch the Future'. This character has knowledge of future events that could either save or destroy the current world of Jujutsu sorcerers. The main characters then have to decide whether to trust this person and how to use the information without causing chaos.
The Jujutsu Kaisen manga is indeed ending. It's been a great run, but all good things must come to an end. The final chapters are bringing closure to the characters and story arcs.
The Jujutsu Kaisen manga has reached its conclusion. The story came to a close with a satisfying ending that wrapped up the plotlines and character developments.