Another trope is the self - rescue. Marinette uses her intelligence and hidden skills to break free from her captors. This shows her strength as a character.
One idea could be that Hawk Moth is behind the kidnapping. He might have discovered Marinette's identity as Ladybug or suspect her. He could use her to try and get the Miraculous. Maybe he offers a trade to Chat Noir, the Ladybug Miraculous for Marinette's safe return.
One common way for Marinette to get revenge in fanfiction could be through her fashion skills. She could design something that makes Lila look foolish. Like creating a dress for an event that has a hidden message or design that mocks Lila's lies when she wears it. It's a more creative and less confrontational way of getting revenge, but still very effective in showing Lila that Marinette is not one to be trifled with.
One interesting 'Marinette kidnapped' fanfiction could be where she is kidnapped by an akumatized villain. In this type of story, the other characters like Chat Noir would have to go on a wild rescue mission. They might face various obstacles and challenges along the way, making for an exciting plot.
In many fanfictions where Gil gets kidnapped, it could be for various reasons. Maybe it's by a rival group who wants to use him as a bargaining chip against his friends. For example, in some stories, Uma's crew might be targeted because they are seen as a threat in the Isle of the Lost. Gil, being a part of that crew, gets kidnapped. Writers often use this plot device to create drama and show the loyalty and courage of the other characters as they try to rescue him.
In these types of fanfictions, Marinette's act of getting hurt protecting Chat can have multiple consequences. It could inspire other characters to be more heroic. It might also make the overall story darker and more complex. For instance, if Marinette is severely injured, the city may be in more danger as Ladybug is out of commission for a while. This then forces other characters to step up their game and fill in the gap. It can also lead to some really emotional and heart - wrenching scenes between Marinette and Chat, as they deal with the aftermath of her injury.
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.
If Marinette was kidnapped, Tikki could be a key factor. She might try to communicate with other Kwamis to get help. Since the Kwamis have some special powers and knowledge, they could work together to find Marinette. For instance, Plagg could use his Cataclysm in a unique way to break through any barriers that are keeping Marinette captive.
It could also be about the challenges they face during the pregnancy. Marinette might have health issues, and Adrien has to be extra careful and supportive. There could be a lot of emotional turmoil as they both grow up faster than they expected. They might also face some judgment from society, but they stand strong together to face it all.