Perhaps a fanfiction where Toothless loses his ability to fly for a while. Hiccup has to come up with a creative solution to help his friend. He might build a new type of device or find a magical cure. This would show their friendship not just in the face of danger but also in dealing with difficulties that affect Toothless' identity as a dragon.
One could write a fanfiction where Hiccup and Toothless meet another version of themselves from an alternate universe. They compare their lives, their relationships with dragons and humans, and learn from each other. This would be an interesting exploration of the characters and how different circumstances could shape them in different ways.
A fanfiction could center around Hiccup and Toothless time - traveling. They end up in a different era where dragons are feared even more than in their own time. They have to find a way to get back home while also trying to change the perception of dragons in this new time period. This would involve a lot of challenges as they would be in an unfamiliar world with different rules and beliefs.
One creative idea could be exploring how their relationship develops in a world full of magic and adventure. Maybe they bond over a shared quest to save their dragon - human community from a common threat. Their mating could be more about a spiritual or emotional connection that is formed through these experiences.
Another fanfiction could start with Merida getting lost in the Viking lands. Hiccup finds her and at first, they have a bit of a misunderstanding because of their different cultures. But as they spend time together, Hiccup helps Merida understand the ways of the Vikings and Merida teaches Hiccup some of her own skills, like how to better track in the forest. Eventually, they become good friends and help each other out in various adventures in the Viking world.
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.
One plot idea could be Fem Hiccup discovers a new ability in Toothless that no one else knew about. For example, Toothless can communicate with a long - lost species of dragons. Another could be Fem Hiccup gets lost in a strange land and Toothless has to use his instincts to guide her back home. And also, a plot where Fem Hiccup and Toothless encounter a powerful enemy dragon and they have to work together to defeat it using their unique bond.
Another plot idea is that a strange illness starts affecting the dragons in Berk. Toothless is one of the first to show symptoms. Hiccup, being the dragon expert, sets out to find a cure. He and Toothless travel far and wide, facing many challenges along the way. They meet other dragon riders from different lands who may or may not be helpful in their quest for the cure. This journey tests their bond and shows how much they rely on each other.
A possible plot could revolve around the female Toothless being injured. Hiccup has to take care of her, and during this time, their relationship deepens. They start to communicate in new ways, and Hiccup learns more about the female Toothless' unique abilities. Or perhaps there is a magical element involved, like a spell that has been cast on the female Toothless, and Hiccup has to break it. This could lead to a journey filled with mystery and self - discovery for both of them.
Well, a plot could involve Hiccup and Toothless getting separated. Hiccup then has to go on a journey to find Toothless, facing many challenges along the way, like bad weather and other dangerous creatures. Or perhaps they find a magical object that gives Toothless some new, unexpected powers. Hiccup then has to help Toothless learn to control these powers. Also, they could be transported to a different time period, and have to find their way back while also dealing with the differences in that era.
Another idea could be that a new and unknown force in their land has the ability to make the impossible happen, like male pregnancy. Hiccup becomes a target for this force for some reason, and Toothless has to protect him not only from the physical threats but also from the social stigma that might come with such an unusual situation. As they face these challenges, their bond deepens and they discover new aspects of their love for each other.
One plot idea could be Fem Hiccup being the only one who can truly understand Toothless's unique abilities and they go on a journey to discover a hidden dragon world that only Toothless can sense. Another could be Fem Hiccup having to protect Toothless from a group of dragon hunters who are after his special powers.
First, you need to have a clear understanding of the characters' personalities. Then, build a plot that naturally leads to the lemon moments. Make sure it fits within the 'How to Train Your Dragon' universe and doesn't feel forced.