Well, if Plagg gets akumatized in fanfiction, it could lead to some really chaotic situations. Plagg's powers are already quite strong as a kwami, and with the akuma's influence, they might become uncontrollable. For example, his cataclysm power could be misused on a large scale, causing destruction all over Paris. Maybe he would turn against Adrien and the other heroes, creating a big rift in their relationships and making it extremely difficult for them to fight back.
The characters' reactions would be quite complex. Adrien would first be in denial, not wanting to believe that Plagg could be akumatized. Then he would feel a mixture of anger and sadness. He might blame himself for not being able to protect Plagg. Marinette as Ladybug would be focused on the bigger picture. She would try to assess the situation quickly and figure out if there are any weaknesses in the akumatized Plagg's powers. Tikki would be worried too, as she has a relationship with Plagg. She might offer some advice to Ladybug based on her knowledge of kwamis.
One possible plot could be that Ladybug is betrayed by someone she deeply trusts, like Chat Noir accidentally revealing her identity to Hawkmoth. This shatters her world and makes her vulnerable to Hawkmoth's akuma. As Ladybug gets akumatized, Paris is in chaos as she starts using her powers in a negative way. The other heroes, like Rena Rouge and Carapace, try to find a way to save her and break the akuma's hold.
Hawkmoth is usually the main antagonist. Since he is the one who akumatizes Marinette in the first place. He takes advantage of her negative emotions, like her insecurities or anger, to turn her into an akuma and use her for his own evil plans.
In a fanfiction scenario where Marinette gets akumatized, it's a really fascinating concept. Marinette is known for her strong will and positive attitude, but if she's akumatized, all that could be flipped. Her akumatized form might be influenced by her repressed emotions, such as her jealousy over Lila's lies being believed so easily. Her akuma - powered actions could start to cause chaos in Paris. And it would be a great opportunity for the other characters to step up and try to save her, not just as Ladybug, but as Marinette. There could be a lot of self - discovery and character growth for everyone involved as they face this new and unexpected threat.
Well, perhaps Gabriel discovers that Adrien has been secretly helping Ladybug and Chat Noir. This betrayal, in his eyes, could lead to his akumatization. As an akumatized villain, he might have the ability to create dark illusions of everyone's worst fears. He uses these illusions to try and break the will of the superheroes and force them to reveal their identities. He could also use his power to turn the citizens of Paris against Ladybug and Chat Noir, making it even more difficult for them to operate.
One possible plot could be Marinette getting akumatized because she feels constantly overshadowed by Ladybug's responsibilities. She might turn into an akuma with powers that are a twisted version of her creativity, like creating chaotic and unmanageable 'designs' that cause havoc in Paris.
In some 'Adrien gets akumatized fanfiction', his akumatization could be caused by a misunderstanding with his father. This could lead to his akumatized form having powers related to control or isolation, like being able to trap people in a sort of prison made of his negative emotions. The story could then focus on how Marinette, as Ladybug, tries to reach out to the real Adrien inside the akumatized form. She might have to dig deep into their relationship and use memories they've shared to break through to him.
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.
If Adrien and Marinette were akumatized, their relationship would become very strained. As akumatized individuals, they would be full of negative emotions which could cloud their judgment. Adrien, who usually has a soft spot for Marinette, might not recognize her in his akumatized state and could even attack her. Marinette, too, would be in a different mental state and might see Adrien as an enemy, forgetting their previous friendship and any budding romantic feelings.