There could be a young girl from a far - off land who has a special bond with a rare type of dragon. She and Hiccup could join forces. She might have unique skills like being able to communicate with dragons without words. And also, an old hermit who has been living alone with his dragon for years. He has a lot of wisdom about the ancient ways of dragon riding and could help Hiccup on his travels.
Astrid is an obvious choice. She already has a close relationship with Hiccup in the original story. Then there could be Ruffnut and Tuffnut's sister, who might see Hiccup in a new light and be attracted to his growing confidence. Also, some new characters from unexplored Viking tribes could be part of it. Maybe a healer from a far - off land who is intrigued by Hiccup's connection with dragons.
One idea could be Hiccup discovers a hidden tribe in a remote jungle. Another could be that he encounters a mythical creature in an uncharted ocean region. Maybe he also teams up with a group of international dragon riders to save a world - spanning dragon sanctuary.
Obviously, Hiccup and Toothless are the main ones. Astrid could also be in it, maybe she tries to figure out what happened to Hiccup and how to turn him back. There could also be other Vikings who are either scared or intrigued by the baby Night Fury that used to be Hiccup.
Hiccup and Rayla might also interact. Rayla is a skilled warrior. Hiccup, with his unique dragon - riding skills, could show her some new combat maneuvers from the air. In return, Rayla could teach Hiccup some of her elven fighting techniques on the ground.
Well, Hiccup is very resourceful. He could use the environment around him to his advantage. If he is locked in a place, he might find a weak spot in the structure, like a loose board or a hole in the wall. And he could call for Toothless secretly. Toothless, being highly intelligent, could find Hiccup and rescue him. Also, Hiccup could befriend some of Viggo's minions and convince them to help him escape.
Toothless is the most likely one. Their bond is so strong that Toothless would sense Hiccup's distress and come to his rescue. He could fly into Drago's hideout and cause chaos to free Hiccup.
Naruto would be a likely ally. Naruto is always open to making new friends and with his strong sense of justice, he would see Thor as someone who can help protect Konoha. Another potential ally could be Kakashi. Kakashi is a very experienced and intelligent ninja. He would be able to quickly assess Thor's abilities and find ways to work together effectively.
He might be shocked at first. After all, finding a baby out of the blue is not an everyday occurrence.
There could be Toothless. Even though Hiccup is now a dragon, his connection with Toothless from his previous human life might still be there. Toothless could play a crucial role in helping Hiccup adapt to his new form.
There may be some extremely creative and boundary - pushing fanfiction out there with this premise, but it's not something that is typically found in the more well - known or widely - accepted "How to Train Your Dragon" fanfiction. Usually, fanfictions in this fandom focus on things like their adventures, friendship, and the development of their bond in a more traditional sense. So, while it's possible, it's not a common plot line.