The characters in 'httyd' would likely have complex reactions to the future in the fanfiction. Hiccup, for example, has always been a forward - thinking character. He would likely be intrigued by the possibilities the future holds, whether it's in terms of dragon - human relations or new inventions. However, he would also be concerned about protecting his tribe and the dragons. Astrid would be more practical. She would assess the potential threats and benefits. The dragons themselves, such as Toothless, would react based on their bond with their human counterparts. If they sense that Hiccup is positive about the future, they might be more open to it, but if there are signs of danger, they would be on high alert.
Yes, there are likely some popular ones. For instance, some fanfictions that explore the relationship between Hiccup and Astrid during the time leading up to HTTYD 2 are quite popular. They might show how their relationship evolves and how they support each other in anticipation of the new threats in the second movie.
Captain America would probably be very reflective. He might see his past self as a reminder of his long journey and how much he has changed. He could try to offer some words of wisdom to his younger self.
Some gods might be entertained. For instance, Hermes, being the trickster god, might enjoy seeing the different and often humorous takes on the gods in the fanfiction.
One interesting fanfiction could be about Toothless having a unique adventure during the time between the first and second movies that the other characters are unaware of until later in HTTYD 2. Another might focus on Hiccup's internal struggles as he anticipates the new challenges in HTTYD 2, all while still dealing with the aftermath of the first movie's events.
Issei could be a bit nervous at first. He might worry about what his classmates will think. But if they show positive reactions, he could become more confident and start sharing more about his writing. However, if they react negatively, he may feel a bit down and might even regret that they saw it.
It's hard to say if it's common. Since Valka is a fictional character, we don't really have data on her fictional reading habits. But in the context of the fandom, it could be seen as something that would be cool if she did, as it would show her interest in the fan - created content.
In my opinion, 'Flight of the Firewyrm' is among the best. It has a really exciting plot where a new type of dragon, the Firewyrm, is discovered and the riders have to figure out how to deal with it. 'Friendship Beyond Boundaries' is good too. This fanfic explores the friendships not just among the human characters but also between humans and dragons in a more profound way. And 'The Dragon Riders' Reunion' is a must - read. It reunites the old dragon riders in a situation where they have to face a new threat together.
Once upon a time in the land of Berk, Hiccup was flying on Toothless when a strange magic portal opened. Out of it came Merida from the land of DunBroch. Hiccup was startled but curious. Merida was amazed by the dragons. They decided to team up. Hiccup showed Merida how to ride Toothless and in return, Merida taught Hiccup some of her archery skills. Together they went on an adventure to save both their lands from a common enemy that was using dark magic.