Maybe a mysterious new character in the fanfiction. This character could be from Adrien's family's past, someone with a vendetta against his family, and decides to start by getting Adrien arrested to disrupt the family. For example, if Adrien's family wronged this character's family long ago, they see Adrien as a target to take revenge on the whole family.
It could be Ladybug. If Adrien turns villain, Ladybug would be the natural antagonist as she represents the good side. Their relationship would be completely flipped from what it was before. She would have to try to stop him from causing more harm, all while probably still having some feelings for the old Adrien.
These fanfictions usually show Adrien with a lot of flaws. He might be painted as being manipulative, using his charm to get what he wants without considering the feelings of those around him. Sometimes, he is shown as being irresponsible, not taking his role as a superhero seriously enough. They really dig into the idea that he is not as perfect as he seems in the original series. They may also show him as being overly jealous, which can cause problems in his relationships. For instance, if he is jealous of another character getting close to Ladybug, he might act out in a negative way.
Nathalie might be a character in these fanfictions too. Given her role in Adrien's life in the original series, she could be involved in the events leading up to his akumatization. Maybe she accidentally triggers his negative emotions. And then there's Gabriel, Adrien's father. His actions or lack of actions towards Adrien could be a major factor in Adrien getting akumatized. So, he could be a key character in the fanfiction, either as someone who realizes his mistake and tries to help or as someone who makes the situation worse.
Well, it depends on various factors. If the fanfic is appropriate and within the bounds of legality and good taste, it could be seen as a normal form of enjoying fan - created content related to a character or story he likes. However, if the fanfic involves inappropriate or unethical content, then it would not be normal or acceptable.
If Adrien were Hawkmoth in fanfic, it could change the dynamics of the story completely. It might explore his internal conflicts and the impact on his relationships with other characters.
He could also be a bit worried. Adrien might think about the responsibilities that come with having a child. He might wonder if they are ready for this big step, considering their own lives and any potential challenges. He would then sit down with Marinette and have a serious conversation about how they are going to handle everything.
One possible reason could be that Marinette has been acting strangely in ways that seem to Adrien to be related to Hawkmoth. Maybe she has been seen in places or at times that are suspicious, like near akuma attacks or where Hawkmoth might be operating from. Another reason could be that someone has been spreading false rumors about Marinette, leading Adrien to believe she has some connection to Hawkmoth.
Perhaps Adrien becomes Hawkmoth because he's been pushed to the edge by Ladybug's rejections. As Chat Noir, he's constantly in love with her but feels unappreciated. The pain of this unrequited love could twist his perception of good and evil. He might think that if he were in control as Hawkmoth, he could make Ladybug see him in a different light. He could use the power to create situations where Ladybug has to rely on him more, or at least understand his pain.
His unwavering determination is another factor. No matter how tough the situation is, Adrien in fanfictions doesn't give up. He is willing to risk everything to protect the people he loves and the city he lives in. This strong will and selfless attitude are what make him a truly badass character in many fanfictions.