Hiccup could try to resist by using his intelligence. He might find loopholes in Dagur's plans or demands. For example, if there are certain cultural or traditional rules that Dagur is using to force the marriage, Hiccup could find ways to show that those rules are being misinterpreted or misapplied.
The relationship can be developed through shared adventures. For example, they could go on a quest to find a rare dragon. Along the way, they face difficulties like harsh weather and dangerous terrains. By relying on each other's skills, they start to bond. Dagur's strength and combat skills combined with Female Hiccup's intelligence and dragon - handling abilities make them a great team. This mutual dependence can lead to deeper feelings.
In such a fanfiction, it could be a really dark and complex story. Maybe Dagur uses threats or some form of blackmail to force Hiccup into this situation. Hiccup, being the strong - willed character he is, might initially resist and try to find a way out. However, if he has no other choice, he could be forced into a marriage that goes against his true feelings. This could lead to a lot of internal conflict for Hiccup, and also a strange and tense relationship between him and Dagur.
One plot idea could be that Dagur and Female Hiccup are forced to team up to face a new threat in their land. They start off not trusting each other but as they go through various challenges together, they begin to respect and then develop feelings for one another. Another could be a story where Female Hiccup has to save Dagur from a dangerous situation and in the process, Dagur realizes how strong and amazing she is, leading to a friendship that could turn into something more.
Well, start by imagining unique scenarios for Dagur and Hiccup's interaction. Maybe have them on a dangerous adventure together or dealing with a common enemy.
Typically, when Dagur kidnaps Hiccup in the fanfiction, it creates a huge crisis. It could be for revenge, to gain some sort of advantage, or just out of pure malice. This event often forces the characters to face their fears and grow stronger.
Well, Archive of Our Own (AO3) also has a great selection of dagur and mala fanfiction. Some of them focus on their adventures together, while others might explore their romantic relationship in more depth. You can search by tags to find the ones that suit your taste best.
The key is to immerse yourself in the 'How to Train Your Dragon' world. Come up with a compelling conflict for Dagur and build the story around that. Pay attention to details and try to capture the magic of the original series.