One common theme is family. Since it's 19 years later, they likely have a family of their own, so stories could revolve around family values, sibling relationships among their children, and how they pass on the traditions of the wizarding world to the next generation.
Another possibility is that it could focus on their adventures together. They might go on some sort of mission or exploration within the wizarding world. It could be related to a new threat that has emerged, and they have to use their combined skills and knowledge to deal with it.
One great fanfiction idea could be that in the years after their wedding, Ron and Hermione take a magical trip around the wizarding world to explore different magical cultures and document them for Hogwarts' library. This would not only strengthen their bond but also contribute to the wizarding knowledge.
One possible story could be that in these 10 months, Ron and Hermione are on a mission together. They face many challenges that test their relationship. Maybe they have to deal with a dark wizard threat and in the process, their bond deepens as they rely on each other's strengths.
A very frequent theme is the challenges they face in their relationship. Because they have different personalities, there are bound to be frictions. Fanfictions love to explore how they overcome these differences and grow closer. Also, family is a common theme. How they start their own family and raise their children, passing on the values they learned from their own experiences at Hogwarts.
I'm not a big fan of such dark fanfictions, but you could try looking on fanfiction.net. They have a large collection of Harry Potter fanfictions, and you might be able to find one with that plot there.
Hermione, on the other hand, could become more vulnerable yet also stronger. She has always been strong - willed, but this experience could break her down initially. However, as she copes with the miscarriage, she might find new depths to her strength. She could become more in tune with her emotions and learn to lean on Ron more, which is a change from her usually independent self. This new dynamic between them would reshape their characters as they support and grow with each other through this difficult time.
Charlie might be a character who has known Hermione for a long time, maybe through some other connections in the wizarding world. He sees Hermione as someone in need of protection from Ron, whether Ron is acting out of his own accord or is being influenced by external forces. In relation to Ron, he is the one who stands against Ron's actions towards Hermione.
Hermione would likely be very angry at first. She is a strong - willed character and being kidnapped would go against all her principles of freedom and rights. She would probably try to reason with Ron immediately, using her logical arguments to make him see how wrong his actions are.
Well, Ron could have developed a more patient side to his personality. He's had experiences that taught him to be more understanding. Hermione may have become more laid - back. Maybe she realized that she was too uptight before. When they reunite, Ron's new - found patience helps him deal with Hermione's still - somewhat - controlling nature. And Hermione's more laid - back attitude allows Ron to feel more at ease around her. It's an interesting dynamic shift that can make for great storytelling in fanfiction.