Perhaps Luke falls due to his own over - confidence. He might attempt a very dangerous and morally ambiguous Jedi technique to try and end a great conflict quickly. But this technique has dark side undertones. As he delves deeper into it, he becomes addicted to the power it gives him, and slowly succumbs to the dark side, losing his way from the path of the Jedi.
In some fanfictions, Luke might fall to the dark side after being betrayed by his closest friends. For example, if he discovers that they have been hiding important information from him that he thinks could have saved lives. This sense of betrayal could push him towards the dark side as he feels abandoned by the light. Also, a powerful dark side user could use mind control techniques on Luke, slowly turning him over time.
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.
One main factor could be the influence of a powerful dark side figure. Such a figure might manipulate Luke's emotions, like his fear or anger. Maybe they prey on his insecurities about his abilities or his place in the galaxy.
One possible scenario could be that Luke is lured by the power promised by a powerful dark side figure. Maybe he's faced with a situation where he believes the dark side can save someone he loves, like if Leia was in mortal danger and the only way he thought he could save her was through dark side powers.
The Emperor or some other powerful Sith lords would likely be involved. They would see Luke as a great prize to turn to the dark side and would use all their cunning and power to manipulate him. Yoda's spirit could also be present, trying to guide Luke from beyond the grave but perhaps being unable to prevent his fall. Han Solo might also play a role, either trying to rescue Luke or being a victim of Luke's new dark side - influenced actions.
Well, obviously Luke himself is a key character. He is the one who is falling to the dark side, so his actions, thoughts, and decisions are central to the story.
In the fanfiction, Luke could be influenced by his family ties to the dark side. If he discovers some hidden connection to Vader or Palpatine that he didn't know before, it might make him question his place on the light side. He could think that joining the dark side is a way to understand his true heritage better and gain more power to protect those he loves in a different way than the Jedi would allow.
One interesting 'dark side Luke' fanfiction could be about him leading a Sith cult. In this story, Luke uses his knowledge of the Force in a twisted way, recruiting followers and causing chaos across the galaxy.
One of the main themes is the struggle between good and evil within Luke himself. In these fanfictions, we see how his inner conflict plays out. Also, the theme of redemption might be present in some, where there is a possibility for Luke to come back from the dark side. And the exploration of the dark side's allure, like the promise of quick solutions to problems compared to the more difficult path of the Jedi.
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.
In some rey falls to the dark side fanfiction, her turn could be due to a sense of betrayal. If she discovers some dark secrets about the Jedi Order or the Resistance, she might feel that the dark side is the only way to get true justice. For instance, if she finds out that the Jedi had some hidden, unethical practices in the past. Then she starts to embrace the dark side teachings and uses her powers in a more aggressive and self - serving way.