Well, start with setting the scene. Maybe it's a sunny day on Berk when Astrid first realizes she's pregnant. She could be out with Stormfly and suddenly feel a bit off. Then, for the plot, you can include how she tells Hiccup. He might be overjoyed and a bit clumsy in his excitement.
One idea could be to focus on how Astrid and Hiccup prepare for the baby. They might start building a new addition to their home on Berk. Hiccup could be super protective, while Astrid is determined to still be involved in dragon - related activities as much as she can until she can't anymore.
There would be a shift in their dynamic as they prepare for a family. Hiccup, who is used to being adventurous, would have to focus more on home and stability. Astrid, while still strong - willed, would become more nurturing. They would need to find a new balance in their relationship, between their old selves and their new roles as parents - to - be.
There is also 'Hiccup and Astrid's Adventure'. This one takes them on a journey to a new land. The way it describes their interactions and how they rely on each other is really engaging. The author has a great writing style that makes you feel like you're right there with Hiccup and Astrid during their adventure.
The kiss is special in fanfiction as it can bring out different aspects of their characters. For Astrid, it might show her softer side that she usually hides. For Hiccup, it could be a moment of confidence, knowing that he has won the heart of such a strong - willed girl. And for the readers, it's a moment that they've been waiting for, a payoff for following their story and seeing their relationship develop from a distance in the HTTYD - inspired fanfiction.
There's also 'The Bond of Hiccup and Astrid'. This fanfiction takes a different approach. It focuses on their love through small, everyday moments. For example, how they train their dragons together and steal glances at each other. It's a very sweet and simple story that really shows their deep connection.
Astrid's character could develop in many ways. She may become more empathetic towards the other mothers in Berk. Before, she was mainly focused on her warrior duties, but now she can relate to the women who have to take care of their families. She might also learn to rely on others more, especially Hiccup, as she goes through the physical and emotional changes of pregnancy.
They could have a journey to find a special herb or something that is believed to ensure a healthy pregnancy in the world of How to Train Your Dragon. This would be an adventure filled with encounters with different dragons and terrains.
Archive of Our Own (AO3) is also a great place. It has a very inclusive and diverse set of fanfictions. Just search for 'httyd hiccup and astrid' and you'll get a bunch of results. The site also has good tagging systems so you can easily find stories with the elements you like, such as adventure or romance.
You can try searching on fanfiction websites like Archive of Our Own (AO3). There are often a wide variety of fanfictions there, and you might be able to find some related to Toothless and Astrid with the'sexy' aspect in different interpretations. Just use their search function and type in relevant keywords.
You can find it on fanfiction.net. There are a large number of stories dedicated to Astrid and Hiccup there. Just use the search bar and type in their names to start exploring.