Her turning evil could also introduce new moral dilemmas for the other characters. Do they try to save her or just stop her by any means necessary? This could lead to internal conflicts within the Avengers. Some might believe she can be redeemed, while others might think she's too far gone. It would add a layer of complexity to the overall storyline.
The dynamic among the Avengers would be completely different. Instead of being a trusted ally, she would become a formidable enemy. They would have to figure out how to deal with her without hurting her too much, especially for those who were close to her like Captain America and Iron Man.
His personality might become more reserved and calculating, like Black Widow. He'd be more cautious in his interactions and less likely to trust easily.
Losing someone she loves deeply could also lead her to turn evil. If, say, Hawkeye was killed and she blamed the Avengers or the world in general for not being able to protect him, she could become vengeful and start to act in an evil way. Grief and anger can often twist a person's moral compass, and Black Widow would be no exception.
He would become more cynical. His once - positive view of the world and people would be replaced with suspicion and hatred. He might start to see everyone as an enemy.
His relationship with MJ would be completely shattered. Instead of being the loving boyfriend, he could become possessive or even abusive. His friends at school would be terrified of him. Ned, who was once his closest friend, would probably try to avoid him or even try to find a way to stop him. And his relationship with the Avengers would turn into enmity. They would see him as a threat and would try to contain or stop him.
The storyline could start with a strange magical accident that creates a portal between the Harry Potter universe and the Marvel universe where Black Widow exists. Harry stumbles through this portal and meets Natasha. At first, they are suspicious of each other but soon realize they have a common goal of fighting evil. As they work together, they develop feelings for each other and eventually decide to get married.
Their relationships with their friends would become extremely strained. Their former comrades would be shocked and saddened by their turn to evil. Naruto and Hinata would no longer be seen as the heroes they once were, and their friends would likely try to bring them back to the light, but it would be a difficult and dangerous task.
If Luke turns to the Dark Side in fan fiction, the story would take a very different turn. The relationship dynamics would be completely altered. His friends like Chewbacca, who had fought beside him, would be in shock. His fall could also inspire other Jedi - in - training to question their own paths. Maybe some would be tempted to follow him into the Dark Side. And the Emperor, if still alive, would have a new tool to use against the remaining Jedi and the Rebellion. He could use Luke to spread fear and chaos, which would be a very different plot from the original Star Wars stories.
The storyline would be greatly affected. In terms of character development, Naruto would have to learn a lot about Sakura, her insecurities, and her strengths. This new understanding could then be carried over when he turns back to his normal self. In the plot, it could also lead to new alliances or enemies. For example, if Naruto - as - Sakura accidentally offends someone who Sakura had a delicate relationship with, it could create new conflicts. Or, on the other hand, he could make new friends by showing a different side of Sakura that others hadn't seen before.
His confidence could turn into overbearing arrogance. Instead of being a source of motivation, it would be a tool to belittle others. His determination might become a stubborn and unyielding obsession with power and domination.
In fanfiction, if Black Star turns evil, it would be a really interesting development. Black Star has always been on a path of growth and self - discovery in the original series. But if he goes to the dark side, his character arc would take a drastic turn. His pride and ambition could be twisted into something malevolent. He may start to see his friends as obstacles to his new - found evil goals. This could lead to some really intense and dramatic storylines, like battles between him and his former comrades, or him causing destruction in the name of his new evil ideology.