There might be a fanfic where Hiccup has to raise a group of baby dragons all on his own. He has to figure out how to feed them, train them, and keep them out of trouble. It could involve a lot of comical and heart - warming moments as he struggles but also learns a great deal about himself and his bond with dragons.
One interesting story could be about Hiccup's adventures in a new land with his dragons that he discovers by accident. Maybe he finds a hidden dragon lair with a rare breed of dragons.
In some fanfics, Hiccup is raised by dragons in a more extreme way. For example, he is separated from his human village at a very young age and grows up completely within the dragon community. This changes his perspective on life, and when he finally reunites with humans, there are a lot of cultural clashes and misunderstandings that he has to navigate while still maintaining his strong connection with the dragons.
There might be a fanfiction where Hiccup is raised not just by Toothless but by a whole group of different dragons. Each dragon teaches him different skills. Some dragons could teach him about flying techniques that are different from what he already knows, while others might show him how to communicate in more complex ways with dragons.
Another plotline might involve the twins' struggle to fit into human society. After being raised by dragons, they would have different values and behaviors compared to normal humans. This could cause conflict when they try to interact with their own kind. They might face prejudice from those who don't understand their dragon - influenced ways, but also find a few who are intrigued and want to learn from them.
The dragons themselves are also important characters. There could be Toothless, who is often Hiccup's closest dragon companion in the original stories. And there might be other dragons like Stormfly, Hookfang, etc., each with their own personalities and roles in Hiccup's upbringing.
One plot idea could be that Hiccup, as a female, has unique ways of bonding with the dragons. For example, she might use her more empathetic nature to understand their needs better than in the original story. Another could be that she faces different challenges in the Viking society which is often male - dominated. Maybe she has to prove herself even more to be accepted as a dragon rider.
One interesting plot idea could be that the dragons start to communicate with Hiccup in a more complex way through their listening skills. For example, they might be able to understand his unspoken fears and desires, and then help him in ways he never expected, like leading him to a hidden treasure that only they knew about because of their unique perception.
One interesting story could be about Hiccup exploring new dragon lands that were previously unknown. He might discover rare dragon species and learn their unique behaviors.
One common theme is identity. The brother raised by dragons often struggles to figure out who he is - is he more dragon or more human? Another theme is acceptance, both self - acceptance and acceptance from the Viking community.
One interesting story could be about a character who discovers a unique bond with a dragon that no one else has. Maybe it's a dragon with special powers and they go on adventures together, facing challenges that test their newfound relationship.
The dragons that raise the twins are also key characters. They could be of different species, each with their own unique traits. For example, a Night Fury - like dragon could be very intelligent and stealthy, teaching the twins how to hunt and move quietly. And a Gronckle - type dragon might be more about brute strength, showing the twins how to stand their ground in a fight.
You can start by looking on popular fanfiction websites such as Archive of Our Own (AO3). It has a large collection of fanfictions from various fandoms, including 'How to Train Your Dragon' which 'hiccup raised by dragons' is related to. Another option is FanFiction.net. It has been around for a long time and has a significant number of stories in this genre.