One possible scenario could be that Leia is manipulated by a powerful dark side user. Maybe through false promises of power or a way to protect her loved ones in a distorted way. Another could be that she becomes disillusioned with the light side due to some great loss or perceived betrayal within the light side forces.
One possible plotline could be that after facing great losses and betrayals, Leia starts to question the light side's values. Maybe the death of a close friend or the destruction of something she holds dear makes her vulnerable to the temptations of the dark side. She might then begin to explore the power that the dark side offers as a means to gain control and revenge.
One possible scenario could be that Luke is lured by the power promised by a powerful dark side figure. Maybe he's faced with a situation where he believes the dark side can save someone he loves, like if Leia was in mortal danger and the only way he thought he could save her was through dark side powers.
The power balance would be severely disrupted. The Rebellion would lose one of its most important leaders, and the Empire or any other dark side - aligned forces would gain a significant advantage. Her knowledge of the Rebellion's strategies and bases could be used against them.
Well, one possibility is that she gets frustrated with the slow progress of the 'good side'. Maybe she sees all the bureaucracy and inefficiency in the fight against the dark forces and decides that the dark side can offer a more direct way to achieve her goals, like a more efficient magical society. But this would be a huge shift from her original character.
In the fanfiction, Luke could be influenced by his family ties to the dark side. If he discovers some hidden connection to Vader or Palpatine that he didn't know before, it might make him question his place on the light side. He could think that joining the dark side is a way to understand his true heritage better and gain more power to protect those he loves in a different way than the Jedi would allow.
In this fanfiction, it could be that Ezra is deceived by a powerful dark side figure. He might start to believe that the Jedi way has failed him and that the dark side can provide a more effective means to achieve his goals. This could lead him to make choices that gradually draw him deeper into the dark side, like using dark side powers and distancing himself from his former Jedi allies.
Well, in this type of fanfiction, perhaps Harry could be lured to the dark side by a new, extremely charismatic dark wizard or witch. This new character might offer Harry power, knowledge, and a sense of belonging that he feels he lacks in the wizarding world. They could manipulate Harry by appealing to his insecurities, such as his status as an orphan and his feelings of being different from other wizards. And then there's the idea that the dark side might seem like a more efficient way to achieve his goals. If Harry is frustrated with the slow progress of fighting Voldemort through traditional means, he could be tempted to use dark magic to end the threat once and for all.
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.
One possible plot could be that Luke is lured by the power the dark side offers. Maybe he gets frustrated with the slow progress of the light side in bringing order to the galaxy. He might see the Sith as more efficient in getting things done. For example, if the Republic is still facing numerous threats and the Jedi are tied by their code not to take extreme measures, Luke could be tempted to cross over.
One possibility is that he is lured by the power promised by the dark side. Maybe he gets frustrated with the slow progress of the light side in fighting the Empire and thinks the dark side can offer a quicker solution to end the tyranny. He could then start using dark side powers like Force lightning and become a feared figure, turning against his former friends.