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.
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.
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.
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.
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.
One aspect of Ahsoka in dark side fanfiction might be her change in appearance. She could start wearing darker robes and her lekku might even seem to have a more menacing look. Her fighting style would also likely change, becoming more aggressive and less about defense. Writers often explore how her relationships with other characters, like Anakin, would be affected. Anakin might be torn between trying to save her and seeing her as a threat.
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 popular theme is the exploration of the dark side's allure for Ahsoka. It might show her struggling with her own darker impulses, like anger or a thirst for power. Another theme could be her isolation as she delves into the darker aspects of the Force, being shunned by her former allies.
Darth Vader is often featured. Given their past connection, it creates a very interesting dynamic in the fanfiction. Another character could be Maul. His own complex relationship with the dark side can interact in various ways with Ahsoka's journey into darkness.