Perhaps a fanfic where a new dragon arrives in Berk during a time of peace. However, this dragon brings with it a mystery that the Hiccup and the gang have to solve. It could be related to an ancient prophecy that the dragon is a key part of, and they must figure out how to fulfill it without causing chaos.
One idea could be a story about a new dragon species that has unique abilities, like the power to control time. The main character discovers this dragon and they form a bond while trying to protect the dragon from those who would misuse its power.
A fanfic could focus on a young Viking who is an outcast but befriends a new dragon that no one has seen before. Together, they embark on a journey to find a lost Viking tribe, facing many challenges along the way, such as harsh weather and dangerous sea monsters.
One idea could be exploring a new type of dragon that has unique abilities, like a dragon that can control time. Another could be a story about a dragon rider who loses their memory but still has an instinctive bond with their dragon. And perhaps a fanfiction where the dragons and riders have to face an otherworldly threat that they've never encountered before.
Popular ideas in HTTYD were dragon fanfic often involve power. For example, a were - dragon might have special powers that others don't. They could use these powers to protect the dragon - human relationship. Also, the concept of a prophecy related to were - dragons can be really interesting. It can drive the plot forward as characters try to figure out if they are part of the prophecy. Friendship between a were - dragon and other characters, whether human or dragon, is also a common theme.
One idea could be that the characters from HTTYD find a strange portal that leads them to the Pokemon world. There, they have to learn how to catch and train Pokemon to find their way back home. Hiccup, being the curious and inventive type, might try to combine the technology of Berk with Pokemon training methods.
One plot idea could be that the reader is a healer who discovers the female dragon injured in the forest. The reader then uses their knowledge of herbs and healing to nurse the dragon back to health. During this process, they form a bond as the dragon starts to trust the reader. Another idea is that the reader is an artist and is fascinated by the beauty of the female dragon. They start to draw the dragon, and the dragon is intrigued by the reader's art, leading to a connection between them. Or perhaps the reader is a lost traveler and the female dragon guides them back to safety, and from there a friendship blossoms.
First, understand the world of HTTYD well. Know the characteristics of different dragons and the relationships between characters. Then, create an interesting plot. Maybe a story about a human turning into a dragon and their adventures in the dragon world. Also, focus on character development. Let the characters grow and change throughout the fanfic.
One idea could be that the dragon's fire power can be used to recharge the Transformers in some way. Another is that the Autobots could learn the concept of flying from the dragons and incorporate it into their own designs. Or perhaps the Decepticons try to capture the dragons to use their power for evil purposes, and the vikings and Autobots have to work together to stop them.
One idea could be to have Toothless meet Jack Frost. Maybe Jack could try to ride Toothless and they could have an adventure together exploring the skies and the wintery landscapes. It would be cool to see how their different powers interact, like Toothless' fire against Jack's ice.
One idea could be that the dragons in HTTYD are attracted to the cold of Frozen's world and they fly there. The people of Arendelle are initially scared but then they learn about the dragons from the dragon riders. Another idea is that Elsa's ice powers somehow have an effect on the dragons, like making their fire breath turn into ice breath for a short time.
One interesting fanfic could be about a young Viking who discovers a new type of dragon with unique abilities and has to learn how to train it in a completely different way compared to the known dragons. Maybe this dragon can change its form or has powers related to the elements in a way not seen before.
There are fanfics that center around the growth and development of anthro dragons. They might start as outcasts in their own world and gradually find their place. These stories often involve character - building and the exploration of friendship. Some might also include elements of mystery, like uncovering ancient secrets related to the anthro dragons.