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.
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.
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.
At first, she might seem conflicted. But as she goes deeper into the Dark Side, she'd become more confident in her new power. Her speech would change too, becoming more cynical. For example, she'd stop believing in the Jedi ideals she once held dear.
Betrayal is a common theme. For example, she might be betrayed by the Jedi Order, which pushes her towards the dark side. Another theme is power. The allure of greater power, whether it's political or related to the Force, can be a factor in her fall.
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.
One interesting 'dark side Ahsoka fanfiction' could be about her being corrupted by an ancient Sith artifact. She might start to use her skills in a more menacing way, turning against her former allies. For example, she could use her lightsaber skills to hunt down Jedi who oppose her newfound dark side ideology.