If Naruto turned to the dark side in a Star Wars fanfic, his shadow clone jutsu could be used in a very menacing way. He could send shadow clones to infiltrate Jedi or Sith strongholds. His Rasengan, with the added dark side energy, might become a more destructive and unpredictable force, like a mini - black hole of sorts in the Star Wars context.
I would recommend 'Darkness Rising in the Galaxy'. This fanfiction has an interesting take on how the dark side could influence different planets and species in the Star Wars universe. It has some great action scenes and a complex plot that keeps you hooked from start to finish.
One possible story could be that Ahsoka, after facing a series of great losses and betrayals, starts to be tempted by the Dark Side. Maybe she discovers some ancient Sith knowledge that makes her question her Jedi teachings. She could struggle with the newfound power it offers and the darker emotions it stirs within her, like anger and vengeance.
One possibility in fanfiction could be that Ahsoka is tricked into the Dark Side. Maybe an old enemy manipulates events to make her feel betrayed by the Jedi Order. This could lead her to explore the power of the Dark Side, believing it to be a way to seek justice on her own terms.
Perhaps there could be a story where Naruto's chakra is seen as a unique form of energy in the Star Wars universe. The Sith see it as a means to enhance their dark side powers. They manipulate Naruto, showing him false visions of his past failures in Konoha, which makes him angry and more susceptible to the allure of the dark side.
One possible fanfiction could be about Ezra Bridger's struggle against the allure of the dark side. Maybe he has a vision of great power that could be his if he turns, but he remembers his friends and the teachings of the Jedi. He battles internally, with the dark side whispering temptations in his ear.
First, you need to understand the Star Wars lore deeply. Know the rules of the Force, the history of the Sith and Jedi. Then, create a unique character who has a believable journey to the dark side. For example, they could start with good intentions but get corrupted. Don't be afraid to explore the darker aspects of the Star Wars universe like the Sith teachings and their power - hungry ways.
In a fanfiction, Ezra might be tricked into joining the dark side by a disguised dark side user. This person could pose as a friend in need, only to lead Ezra down a dark path. They could manipulate his insecurities and his desire to be a stronger Jedi.
A fanfiction idea could be that Ezra, in his search for a way to defeat a great enemy, stumbles upon an ancient dark side temple. Inside, he is influenced by the dark side presence. His connection to the light side starts to fade. He becomes more aggressive and less empathetic, using his powers for his own gain rather than the greater good, and his relationships with his former allies become strained as a result.
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.