One possible plot could be that Luke is disillusioned with the Rebellion after some major setbacks. Maybe he discovers some secrets about the Rebellion that make him question their motives. So, he decides to join the Empire in the hope of bringing about change from within. He might start off by using his Jedi skills to gain favor among the Imperial ranks.
Another possibility is a group of Imperial scientists who are conducting unethical experiments with the Force. They see Luke as a prime specimen and try to control him. They would be the main antagonists as they try to use Luke for their own immoral purposes rather than allowing him to pursue his own agenda within the Empire.
If Luke joined the Empire in a fanfic, it would be a complete deviation from his original path. He might use his Force abilities to rise quickly within the Empire's ranks. However, his friends like Han and Leia would likely become his enemies, leading to intense and tragic confrontations.
In the 'Luke Joins the Academy Fanfiction', it's possible that Luke discovers a hidden talent within himself while at the academy. This could lead to him getting special attention from the teachers or being selected for a unique project. He may also develop a rivalry with another student which adds drama to the story.
If Percy joined Luke, it might complicate the dynamics. Maybe they'd have to face new challenges together or deal with the reactions of other characters. It could really shake things up!
This would be a huge twist. It might mean Luke is seduced by the dark side's power or has some ulterior motive for joining Vader. It could change the course of the entire story.
Well, one possibility is that Luke initially struggles with the strict rules and hierarchies in the imperial academy. He might face challenges from other students who are more loyal to the Empire's ideals from the start. But as time goes on, he could start to see some aspects of the academy's teachings that he can use for good, even if it's against the Empire's intentions.
If Luke joins the Dark Side, it would completely change the dynamic of the Star Wars universe. His friends would be shocked and heartbroken. Leia, for instance, would probably try to bring him back. The Rebellion would lose a great hope and the Empire might gain an unexpected and powerful ally. It could also lead to a different kind of struggle within the galaxy as those who once believed in Luke now have to face him as an enemy.
It could be the headmaster of the imperial academy. They would be in charge of making sure all the students adhere to the Empire's values and teachings. They might see Luke as a potential threat to their regime within the academy and constantly try to undermine him or turn him into a loyal imperial subject.