Well, it could strengthen their relationship. Adrien, as Chat Noir, has always been in a similar situation. So he can really understand what Marinette is going through. They might start to rely on each other more and share their experiences of having a double life.
Well, it really depends on how the author writes it. If the overprotectiveness is written in a way that respects Marinette's agency, it could be a cute and endearing aspect of their relationship. But if it comes across as controlling, it might make Marinette resent Adrien, and then they would have to work through those issues to have a healthy relationship.
Well, it could be a bit rocky at first. Adrien might be in disbelief and not know how to act around Marinette. But as time goes on, he could start to see all the times Marinette has shown the same qualities as Ladybug, like her courage and kindness. This realization would slowly bring them closer. For example, he might remember all the times Marinette has stood up to bullies at school, just like Ladybug does against villains. Eventually, they would have a deeper, more meaningful relationship.
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.
In some fanfictions, Marinette gets over Adrien when she discovers new hobbies. For instance, she might take up painting or cooking. These new activities bring her joy and a sense of accomplishment. As she spends more time on them, she creates a new life for herself that doesn't revolve around Adrien. This helps her to let go of her old feelings for him.
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.
The situation would force them to develop their problem - solving abilities. They'll have to deal with financial issues, housing problems maybe, and the social implications. Adrien might have to learn how to earn money in a more stable way, and Marinette could explore ways to balance her creative pursuits with motherhood. This would all contribute to a major transformation in their characters.
They would become even closer. Their love would grow deeper as they are about to start a family together. There would be more tender moments between them.
The kittens can act as a catalyst for their relationship. As they play with the kittens, they might start to see each other in a new light. Marinette could see Adrien's soft side when he coos at the kittens. And Adrien might notice Marinette's nurturing nature. This newfound understanding can deepen their feelings for each other. They could start to be more open and honest with each other because of these shared kitten - related experiences.
It could bring them closer. Adrien seeing Marinette in this vulnerable and creative state might make him more attracted to her.
In many fanfictions where Adrien and Marinette are 'just friends', it often shows a different side of their dynamic. It might focus on their platonic adventures, like teaming up to solve a school mystery without any romantic undertones. This can be refreshing as it explores their characters beyond the typical love - interest aspect.