Sure. There's a fanfiction where Luke discovers a hidden Sith temple that has the power to reverse the light - dark side balance in a person. He enters out of curiosity but gets trapped. The temple starts to slowly turn him to the dark side. As he changes, his friends sense it and have to decide whether to try to save him or destroy him, which is a really unique take on the concept.
One possible plot could be that Luke is lured by the power the dark side offers. Maybe he gets frustrated with the slow progress of the light side in bringing order to the galaxy. He might see the Sith as more efficient in getting things done. For example, if the Republic is still facing numerous threats and the Jedi are tied by their code not to take extreme measures, Luke could be tempted to cross over.
Luke's friends from the light side could also be important. Characters like Leia, Han Solo, or Chewbacca. Their reactions to Luke's turn and their attempts to bring him back would be significant aspects of the story. There could also be new characters created specifically for this novel, perhaps some Jedi who were thought to be dead but are actually in hiding and oppose Luke's new path.
There's a fanfiction where Luke discovers a hidden Sith temple on a remote planet. Instead of destroying it immediately, he decides to study it to understand the Sith better. This leads to some intense internal struggles as he battles the dark side's allure while trying to gain knowledge to help the Jedi. It's unique because it flips the typical 'destroy all things Sith' narrative.
One of the main themes could be the struggle between good and evil. Luke Skywalker is typically a symbol of the light side, so exploring his journey towards the dark side would likely involve his internal battle with his own moral compass. Another theme might be the allure of power that the dark side offers and how it can corrupt even the most noble of characters like Luke.
One interesting 'Luke Skywalker dark side' fanfiction could be where Luke turns to the dark side after being constantly betrayed by the New Republic. In this story, he might use his newfound dark side powers to take revenge on those who he feels have wronged him. He could form an alliance with remnants of the Empire and become a powerful and feared Sith - like figure in the galaxy.
It could be the remaining Jedi. Since Luke has joined the dark side, the Jedi who still uphold the light side would be his natural antagonists. They would see him as a threat to all they stand for and would try to stop him from spreading the influence of the dark side. For example, Leia, if she still adheres to the Jedi teachings, would be in direct opposition to Luke.
Maybe in the fanfiction, Luke witnesses something so devastating that he loses faith in the Jedi way. For example, if the Jedi Order fails to prevent a great catastrophe. This could push him towards the Dark Side as he seeks a more radical solution to bring order. He might start using aggressive and unethical means, like Vader did, believing it's for the greater good.
Sure. There's a fan fiction where Han and Luke are sent on a diplomatic mission to a planet that is on the verge of joining the Empire. But it turns out to be a trap set by Darth Vader. They have to use their wits and Luke's Force powers to escape and expose the Empire's true intentions to the planet's leaders.
One popular 'Luke dark side fanfiction' is 'The Dark Path of Luke Skywalker'. It explores what would happen if Luke fully embraced the dark side after his encounter with Vader. Another is 'Luke's Fall to Darkness', which delves into the psychological changes that lead him to turn.
If Luke Skywalker turns to the Dark Side in fan fiction, one possibility is that he could become a powerful and feared Sith Lord. He might use his Jedi skills in a perverted way, like using the Force to dominate rather than protect. His relationship with his friends would be severely strained. Leia, for example, would be heartbroken and might try to bring him back, but it would be a very difficult task. Han Solo would also be in a tough spot, having to choose between his loyalty to Luke and his own sense of right and wrong.