They might start by learning about each other's cultures. Hiccup could teach Elsa about Viking traditions like dragon training and their feasts. Elsa could introduce Hiccup to the Arendelle court and its formalities. They would also have to find a middle ground for things like celebrations. For example, they could combine the Viking bonfires with Arendelle's ice sculptures for a unique wedding anniversary celebration.
The best elements would include their respective powers. Hiccup's dragon - training skills and Elsa's ice magic can create some really cool interactions. For example, they could use their powers together to fight off an enemy or to create something beautiful for their kingdoms. Another element is the cultural clash and subsequent understanding. Hiccup's Viking ways and Elsa's royal Arendelle upbringing can lead to interesting situations where they learn from each other.
First, understand the characters well. Hiccup is from 'How to Train Your Dragon' and Elsa from 'Frozen'. For a married fanfiction, start with how they meet. Maybe it could be in a magical land that combines the worlds of Berk and Arendelle. Then, focus on their relationship development. Show how they learn about each other's strengths and weaknesses. For example, Hiccup's ability to bond with dragons could amaze Elsa, and Elsa's ice powers could be useful in Berk's cold climate. Finally, add some conflict, like a villain who wants to break their marriage or a misunderstanding between them to make the story more exciting.
A plot twist might be the discovery that they are part of an ancient prophecy. They initially got married for love, but then find out that their union is crucial for saving both their worlds from a great evil. Maybe there's an evil sorcerer who has been waiting for them to marry so he can steal their combined powers. So they have to figure out how to fight this sorcerer while also dealing with the new pressures of their relationship.
Their relationship might start with curiosity. Hiccup would be curious about Elsa's ice powers and Elsa about Hiccup's connection to dragons. As they interact more, they start to respect each other's abilities and personalities. This mutual respect turns into friendship, and then gradually into love. The news of the baby would strengthen their bond as they now have a shared future to look forward to. They would support each other more, with Hiccup protecting Elsa during her pregnancy and Elsa using her powers to help Hiccup in his adventures.
One possible antagonist could be a jealous sorcerer. He might be envious of Hiccup and Elsa's relationship and the power that their unborn child is said to possess. So he tries to harm Elsa during her pregnancy to stop the child from being born. Another could be some of the traditionalists from their respective kingdoms. They don't approve of their relationship and see the pregnancy as a threat to their old ways. They might try to separate Hiccup and Elsa, which would put Elsa's pregnancy at risk.
One possible plot could be that Hiccup, while on a journey with Toothless, somehow gets transported to Elsa's world. He stumbles upon Elsa as she is trying to control her powers in a difficult situation. Hiccup, with his experience dealing with dragons, offers her a different perspective on handling her powers. They gradually grow closer as they share their stories and in a moment of deep connection, they share a kiss.
Family and legacy is also a common theme. Elsa's marriage may lead to starting a family, and this brings up questions about the future of her kingdom. Fanfictions might explore how she will pass on her powers, or what kind of rulers her children will be. It's about building a new family unit and how that impacts the existing family of the kingdom.
Hiccup is adventurous and curious. He would be intrigued by Elsa's ice powers and her reserved nature. Elsa, on the other hand, is cautious and has been through a lot with her powers. Hiccup's boldness might initially make her a bit uncomfortable, but his kindness would draw her in.
Well, perhaps Hiccup would be really nervous when meeting Elsa's parents. He might show them his dragon - riding skills to prove he's worthy. Maybe they would initially be skeptical of him because he comes from a different world with dragons, but then come to see his good heart.