He could be shocked at first. I mean, he has been so close to Marinette all this time without realizing she was Ladybug. His reaction might include disbelief and then a quick acceptance as he starts to piece things together in his mind.
The relationship between Adrian and Marinette is full of ups and downs in the original story. So, seeing Adrian finally take the step to propose adds a new and exciting dimension. It's interesting to see how their dynamic changes from being friends or just having a crush on each other to something more serious. Also, the way Adrian plans the proposal, whether it's a grand gesture or a simple but heartfelt one, can be really engaging.
One great Marinette x Adrian fanfiction is 'A New Day'. It shows their relationship developing in a really sweet way. Another is 'Love in Paris' which has some interesting plot twists. 'Hidden Feelings' is also good as it delves deep into their unspoken emotions. 'Under the Stars' is a beautiful story that focuses on their moments together. And 'The Dance' is a fun read with a lot of cute interactions between them.
One possible scenario could be that Adrian plans an elaborate, romantic proposal. He might take Marinette to their special place, like the park where they first met, and get down on one knee surrounded by beautiful flowers and candles. Another scenario could be that he proposes during a big event, like a masquerade ball where they are both dressed up. He could remove his mask and present the ring with a big, heartfelt speech.
A major theme is 'slow - burn romance'. Writers love to gradually build up the relationship between Marinette and Adrian. There are also stories centered around 'shared dreams'. Maybe they both have a dream for Paris or for their future together. 'Adventure - based love' is another, where they go on adventures together and their love grows during those experiences.
The pregnancy in the fanfiction might also be a catalyst for character growth. Sydney could become more assertive in protecting her unborn child and her relationship with Adrian. Adrian, on the other hand, might have to step up and be more responsible, leaving behind his more carefree ways.
Maybe the fanfic starts with Adrian being a pro at breakdancing and Marinette being a beginner. Marinette is in awe of Adrian's skills. He offers to teach her. As they have their breakdance lessons, there are cute moments like when Marinette keeps tripping and Adrian catches her. Slowly, Marinette improves and they end up performing together at a local event, impressing everyone there.
One interesting plot could be Adrian's initial shock and then his realization of all the times Marinette's behavior as Ladybug made sense in her civilian form. For example, her courage as Ladybug might be seen as her standing up to Chloe in her Marinette guise.
In this breakdance fanfic, Adrian's character might develop a deeper sense of connection with Marinette. As they share this new passion for breakdancing, he might start to rely on her more and value her opinions. Marinette would likely develop a stronger sense of self - esteem. The physicality of breakdancing would force her to be more in tune with her body and her abilities, which would translate into her being more confident in other aspects of her life as well. Also, they both might learn about teamwork and cooperation as they create breakdance routines together.
Relationships are a big theme. It could be her relationship with her partner getting stronger or more complicated. Also, her relationships with friends and family might change as they all adapt to the situation. Another theme could be her growth as a person. The experience of pregnancy might make her more responsible and mature in the fanfiction.