I'm sorry, but 'lemon' in fanfic often refers to adult content, so I can't recommend such fanfics. However, there are many great non - adult Hiccup and Ruffnut fanfics out there. You can try searching on fanfic platforms like Archive of Our Own and filter for appropriate ratings.
Another theme is growth. In many fanfics, both Hiccup and Ruffnut grow as individuals while also growing closer as a couple. For example, Hiccup might help Ruffnut see the value in strategy, and Ruffnut might help Hiccup be more bold and take risks. There are often adventures that they go through together which contribute to this growth. Also, the theme of acceptance is prevalent. They accept each other's flaws and quirks, which is a big part of their relationship development.
Adventure is also a big one. They often go on quests together in fanfiction, facing challenges and relying on each other. For example, in some stories, they might be on a mission to find a lost dragon or a hidden treasure.
There is a fanfiction titled 'Hiccup and Ruffnut: Dragon Riders' Allies'. In this one, they have to work together to defend Berk from a new threat. It's full of action scenes and also some really interesting character development for both of them.
One great httyd hiccup x ruffnut fanfic is 'A Different Bond' on FanFiction.net. It explores a unique relationship between Hiccup and Ruffnut that develops over time through their adventures.
One common theme is the idea of unexpected love. Since they seem like an unlikely pair at first, many fanfictions play on the idea that love can develop in the most unexpected ways. For example, they might start off as just friends or even rivals and then gradually fall in love.
A great plot idea could be that Hiccup discovers a new type of dragon behavior and Ruffnut is the only one who believes him at first. Together, they study the dragon and try to convince the rest of the group about their discovery. Or perhaps there's a plot where Ruffnut accidentally gets into trouble with a group of hostile Vikings and Hiccup has to rescue her using his unique knowledge of dragons and the land.
One interesting plot could be that Hiccup and Ruffnut are on a quest together and Ruffnut's brash nature constantly clashes with Hiccup's more strategic thinking. But along the way, they start to understand each other better. For example, they might be searching for a rare dragon that only Hiccup has the knowledge to track, and Ruffnut has the physical skills to help in the dangerous terrain.
For Hiccup, start with her insecurities. Maybe she doubts her leadership skills as a female in a male - dominated dragon - riding world. Then, as she interacts with Ruffnut, she could gain more confidence. For example, Ruffnut might encourage her to be more assertive in a certain situation, like when dealing with a difficult dragon. And for Ruffnut, her development could be about becoming more empathetic. She could learn from Hiccup how to think about others' feelings.
One great ruffnut and hiccup fanfiction is 'The Unlikely Bond'. It shows a unique friendship developing between them in a post - dragon - training era.