A time - traveling device could be discovered in Berk's ancient ruins. When activated, it starts to pull parts of the past and future together. This causes chaos as different versions of characters meet each other. For example, a young Hiccup meets his older self. They have to figure out how to stop the device and in the process, learn valuable lessons about their own growth and the development of Berk and its relationship with dragons.
One idea could be that an old enemy from the past resurfaces in the future, but with new and more powerful abilities. The dragons and riders have to combine their old - school knowledge with the new technology they've developed over time to defeat it.
Perhaps a character from the past gets accidentally sent to the future. They are shocked by the changes in Berk and how the relationship between humans and dragons has evolved. They then use their knowledge of the past to help solve a future problem, like a new dragon disease that the future riders are struggling with. The story could be about how the past and future work together to overcome this challenge.
One plot idea could be Merlin traveling to the future and finding that magic has been completely forgotten. He then has to figure out a way to re - introduce magic without causing chaos. Another could be a future descendant of Merlin's friends coming back to the past and accidentally changing the course of history, so Merlin has to fix it. A third idea is that in the future, there is a new dark magic threat that can only be defeated with the knowledge Merlin has from the past.
One idea could be a time - traveling hero from the past who gets stuck in a high - tech future world and has to adapt to new technologies while using his old - fashioned skills to solve problems. For example, a medieval knight in a world of flying cars and laser guns.
Perhaps past versions of the Crystal Gems meet their future selves. They could be shocked by how much they've changed, or they might learn valuable lessons from each other. The past Gems could see how their actions in the past led to the future they now inhabit, which could be a really interesting exploration of cause and effect.
Toothless is another great candidate. As Hiccup's dragon, he has a unique bond with his rider. In a past - meets - future story, he could be the one to sense the disruptions in time. He might also meet his descendants or ancestors in the future or past dragons, which could lead to some really interesting interactions. For example, an ancient dragon from the past might teach Toothless a long - lost skill that helps them in a future battle.
One idea could be that Riley and Maya are now teachers at their old school. They have to deal with a new generation of students who are facing different but equally challenging problems. It would be interesting to see how they use their own experiences growing up to guide these kids.
The fanfiction might focus on how the relationships between the characters change when the two worlds of HTTYD and HTTYD2 collide. For example, Astrid might have to adapt to new ways of dragon riding she sees in HTTYD2, and this could cause some friction or growth in her relationship with Hiccup. It could also involve the dragons from the first movie learning new skills from the HTTYD2 dragons.
Maybe the main character in the HTTYD runaway fanfiction runs away due to a misunderstanding. They think they've accidentally caused harm to their dragon or their village. As they run, they discover a long - lost dragon lair filled with ancient secrets. This discovery could lead them on a journey to redeem themselves and bring back valuable knowledge to their people.
A cool plot twist could be that future Obito is actually there to stop past Kakashi from making a certain decision that would have far - reaching negative consequences. Another one might be that past Kakashi discovers that future Obito has a hidden agenda that is not what it seems at first.
One interesting plot idea could be Hiccup and Astrid going on a secret adventure to a new, uncharted island. They face new dragons and have to work together to survive. Another could be a story where they have to deal with a rift in their relationship due to a misunderstanding, like Astrid thinking Hiccup is spending too much time with a new dragon rider. A third idea is a time - travel plot where they go back in time and have to change something in Berk's history to save the future.