One plotline could be Padme's discovery of a long - forgotten Sith artifact. The artifact has the power to corrupt those who come in contact with it. Padme, in her quest for knowledge and power to change the galaxy, finds and unlocks the artifact's power. Slowly, it starts to change her, making her more aggressive, power - hungry, and willing to sacrifice the well - being of others for her own ends.
One way could be to show Padme gradually losing faith in the Jedi Order. Maybe she discovers some dark secrets within the Order that make her question their motives. For example, if she finds out that the Jedi have been involved in some unethical political manipulations in the name of peace. This could start to chip away at her idealistic view of the light side and nudge her towards the dark side.
Their relationship becomes more possessive. In the Dark Side, Anakin's love for Padme could turn into an obsessive need to control her. He might see her as his possession rather than an equal partner.
In this kind of fanfiction scenario, it would be a huge shock to the Star Wars universe. Obi - Wan is known for his strong connection to the light side. If he turned, perhaps his relationship with Anakin would have been drastically different. Instead of being a mentor, he might have been a rival or even a corrupting influence on Anakin.
Well, if Obi Wan turned to the dark side in fanfiction, it would likely shake up the dynamics between him and the other Jedi. It might also change the outcome of many key battles and events in the Star Wars universe.
One idea could be that Anakin's fall to the Dark Side causes him to try and make Padme a Sith as well. He might use his newfound power to manipulate her, believing that together they could rule the galaxy. For example, he could start by isolating her from her friends and allies in the Jedi Order and the Republic, making her more dependent on him.
Well, at first, they might seem closer as they are now both part of the same 'dark' world. But soon, the dark side's influence of greed and power - hunger would start to drive a wedge between them. Anakin, with his already tumultuous relationship with power, might try to dominate Ahsoka. Ahsoka, having been dragged into the dark side against her will perhaps, would resent Anakin for it. Their relationship would be a volatile mix of shared darkness and individual power struggles.
Ezra would become more ruthless. His once kind and empathetic nature would be replaced with a cold, calculating demeanor. For example, he might not hesitate to sacrifice innocent lives if it served his purpose. His relationships would also change drastically. His friends would become either obstacles to be removed or pawns to be used.
Perhaps Anakin manipulates Obi - Wan's emotions towards him. Anakin could play on their brotherly bond and twist it. He might make Obi - Wan think that by joining the dark side, they can save more lives together. Anakin could also introduce Obi - Wan to some dark side teachings that seem appealing at first glance.
If Anakin hadn't turned, the Sith's plans might have been foiled. The balance of power would have remained with the Jedi, and galactic conflicts could have been avoided or resolved differently.