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.
Fanfiction.net is also a good place to search. There are numerous fan - created stories on this platform, so you might be able to find some interesting Hiccup and Elsa love fanfictions. Just use the search function and type in their names.
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.
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.
Well, perhaps there could be a fanfiction where Hiccup and Elsa are both summoned by a powerful wizard to help with a prophecy. They don't trust each other at first, but as they face the challenges set by the wizard, which include tasks that require both fire (from Hiccup's dragon) and ice (Elsa's power), they start to respect and care for each other.
Hiccup is the protagonist who embarks on the meeting with Elsa's parents. He's brave and curious. Elsa's parents, on the other hand, are the ones he's meeting. They are likely to have certain expectations and reactions. There may also be other secondary characters from either the How to Train Your Dragon or Frozen universes that could make an appearance and influence the encounter between Hiccup and Elsa's parents in the fanfiction.
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.
A plot could involve Elsa's ice powers acting up during her pregnancy. Hiccup, being from a more technological and dragon - friendly world, tries to find ways to help her control it. They might seek the help of Toothless and other magical creatures in their world. Maybe they face opposition from some of their people who are not happy about their union, especially with a baby on the way. But they stand strong together and prove that love can bridge any gap.