She may feel a mix of emotions. On one hand, she's relieved that Adrien is there to protect her from the creep. But on the other hand, she might be a bit embarrassed because she's always trying to be strong on her own. However, as the situation unfolds, she would probably start to feel more confident with Adrien by her side, and this could lead to her relying on him more during that moment in the fanfiction.
Marinette might be initially shocked when Adrien steps in to protect her. She could be very grateful and show it with a shy smile or a simple 'Thank you.'
Another reaction could be that Marinette pretends to cooperate with Adrien at first. By doing this, she can buy time and look for an opportunity to escape or get help. She might act as if she is okay with what is happening while secretly planning her next move, like leaving a clue for someone to find her or finding a way to disable Adrien temporarily.
Well, it could start with the creep harassing Marinette in some way, like following her around or making inappropriate comments. Adrien, being the hero that he is, notices this. He could then use his physical strength if needed, perhaps getting in a position to block any unwanted advances. He might also call for help from their friends or even the authorities if the situation gets really bad. And all of this would be a great display of his love and care for Marinette, even if he hasn't fully realized his true feelings for her yet in the context of the fanfiction.
Marinette could react with disbelief and assume it's some sort of joke at first. But when she realizes Adrien is serious, she might start to get really nervous. She could start fidgeting with her hands or her hair. If she's in the middle of doing something, like working on a design, she might drop her tools in surprise. Once the shock wears off, she would most likely be very happy and accept his invitation, but it would be a very flustered and excited acceptance.
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.
Marinette would likely be very frightened at first. She might scream or try to fight back. After all, being kidnapped is a terrifying situation.
In some fanfictions, Marinette might get over Adrien by focusing on her own self - growth. She could start to pursue her own dreams and interests more passionately. For example, she may pour all her energy into her fashion design career. By achieving success in this area on her own terms, she realizes that she doesn't need Adrien to feel fulfilled. This new - found confidence helps her move on from her feelings for him.
After getting married, they would become more open and trusting with each other. Since they know each other's identities as Ladybug and Chat Noir, there would be no more secrets between them. Their relationship would be more stable and they would support each other even more in their daily lives and superhero duties.
Alya would probably be super excited and start planning everything from baby showers to future playdates. She'd be there for Marinette every step of the way, giving advice and support. Nino might be a bit more reserved at first but would soon warm up to the idea and be a great source of comfort for Adrien, like helping him pick out baby clothes or build nursery furniture.
Another difference is how they interact with other characters. In canon, their interactions with other characters are sometimes influenced by their unspoken romantic feelings for each other. In the 'just friends' fanfiction, they can form more independent relationships with others. For instance, Marinette could have a closer friendship with another girl in school without any jealousy from Adrien, which is different from the canon where there's often some form of romantic jealousy involved.
Marinette could first be very confused as to why Adrien would think that. Then she would likely be angry. After all, she is actually fighting against Hawkmoth as Ladybug. She would probably start gathering evidence to prove her innocence, like showing Adrien her normal life activities that are completely opposite to what Hawkmoth stands for.