In fanfiction, Anakin joining the Dark Side often has complex motives. It could be due to his fear of losing Padmé. The Dark Side might seem to offer him a way to save her, so he succumbs to its power.
Another plot is Anakin's search for greater power in fanfiction. He believes that the Jedi Order is holding him back from reaching his full potential, and the Dark Side seems to offer unlimited power. So he makes the fateful decision to join it. This often involves his internal struggle between the light and the dark within him, which is a great source of drama in these fanfictions.
One possibility could be that Batman's sense of justice becomes warped. He might start using more extreme and unethical methods to 'clean up' Gotham. For example, he could be more brutal with criminals, foregoing his usual no - kill rule. His relationships with his allies would also be severely strained. Alfred would be deeply disappointed and the Bat - family might split apart as they try to oppose his new, darker path.
Betrayal is also a big theme. He betrays the Jedi Order, his friends, and ultimately himself. His relationship with Obi - Wan, for example, is often explored in these fanfictions as a relationship that is shattered by his turn to the dark side. And there's the theme of internal conflict. Anakin is constantly at war with himself, his good side fighting against the allure of the dark side, which is a central aspect in many of these stories.
Fanfiction usually develops Anakin's character by showing his relationships in a new light. His bond with Palpatine could be shown as more complex, with Palpatine slowly manipulating Anakin over a long period, preying on his weaknesses like his desire for power to save Padmé. This makes his turn seem more gradual and believable.
If Anakin didn't turn to the dark side in fanfiction, it's conceivable that he would have become a true hero. He could have trained more Jedi, passed on his skills and wisdom, and maybe even prevented the rise of new villains. The story would be filled with hope and optimism instead of the darkness that followed his fall.
The fanfiction could explore an alternate timeline where Anakin has stronger support from the Jedi Council. If they recognized his potential and didn't hold him back, he would be more likely to stay on the light side. It could also show how his relationships, like with his mother or with Padmé, could be developed in a way that keeps him grounded in the light. For instance, if his mother was saved in a different way and he didn't have that anger and fear, it would help him resist the dark side.
In RWBY fanfiction, the 'dark side Ruby' concept can be really interesting. It often explores the idea of what would happen if Ruby, who is usually the optimistic and pure - hearted leader, were to be pushed to her limits or corrupted in some way. It could be due to a great loss, like losing her team members, or being influenced by some dark force within the RWBY universe.
In 'tmnt dark side of the sun fanfiction', the relationships between the Turtles themselves might be developed in different ways. For example, they could face internal conflicts due to the harsh conditions of the 'dark side of the sun' setting. Their bond as brothers might be tested, and we could see how they overcome or succumb to these challenges.
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.
In this fanfiction, it could be that Rey has some personal losses that make her turn. She might lose someone dear to her and in her grief and anger, she decides that the dark side can give her the strength to prevent such losses in the future. She then starts learning the ways of the dark side, which changes her relationships with her friends.