She could be driven by a sense of betrayal. Maybe she discovers that the Jedi Order has been hiding something crucial from her, like a dark secret about her past or a false promise they made. This could shatter her trust in the light side and make her vulnerable to the temptations of the Dark Side.
Ahsoka might be exiled from the Jedi Order for reasons she doesn't fully understand. In her solitude, she meets a mysterious figure who has ties to the Dark Side. This figure begins to teach her alternative ways of using the Force that are more in line with the Dark Side. Ahsoka, feeling betrayed by the Jedi, starts to consider these new teachings.
Another plot could involve a powerful Sith Lord who manipulates Luke. The Sith Lord could use Luke's insecurities, like his fear of not being strong enough to protect his friends. He could be tricked into believing that the Dark Side would give him the power he needs, and slowly turn to the dark side as a result.
It could be Darth Sidious. He is always looking for powerful allies. If he senses Ahsoka's potential and her growing disillusionment with the Jedi, he might manipulate her into joining the Dark Side. His cunning and power would make him a formidable antagonist in this scenario.
If Rey turns to the Dark Side in fanfiction, one possibility is that she becomes a powerful and feared Sith. She might use her newfound dark powers to seek revenge on those who she believes have wronged her in the past. Maybe she would target the Resistance, seeing them as the ones who failed to fully understand or support her. Her connection to the Force could take a dark turn, with her using it for domination rather than protection.
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.
The influence of a powerful dark side user who targeted her specifically. This user could manipulate her emotions, play on her insecurities and gradually turn her towards the dark side. They might offer her knowledge or power that she couldn't resist, slowly corrupting her view of the Force.
She might start by becoming disillusioned with the Jedi Order. Maybe she discovers some secrets that make her question their ways. Then, she could be lured by the power the Dark Side offers, like Darth Vader was. She'd likely start using more aggressive and unethical tactics in combat and in her relationships.
In a fanfiction, Ezra could be exposed to a dark side cult. They convince him that the Dark Side offers a more efficient way to bring order to the galaxy. He then starts to use dark side techniques in his fighting and decision - making. His fall to the Dark Side could be a long and tragic process, with him losing his moral compass along the way.
She might be tempted by the Dark Side if she discovers a hidden truth about the Jedi Order that she can't accept. So she turns to the Dark Side thinking it's a better alternative. For instance, if she finds out that the Jedi have been hiding some dark secrets about the Force, it could push her over the edge.