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.
Marinette would likely be very frightened at first. She might scream or try to fight back. After all, being kidnapped is a terrifying situation.
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.'
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.
One possible motive could be that in the fanfiction, Adrien is being controlled by some dark magic or an evil force. This external influence makes him act against his true nature and kidnap Marinette. For example, perhaps a villain has cast a spell on him to use him as a tool to get to Marinette, who might have some special power or knowledge that the villain desires.
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 could use her wits. If she's tied up, she might be able to find a sharp object nearby to cut the ropes. For example, if she's in a room with some old furniture, there could be a nail or a broken piece of wood that she can use.
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.
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.