A really interesting concept could be that the reader is from the future. They accidentally time - travel to the world of 'Yona of the Dawn'. With their knowledge of future technologies (even if it's just basic things like making better tents or more efficient ways to store food), they contribute to Yona's cause. The reader could also introduce new ideas about leadership and equality that are ahead of their time in the 'Yona of the Dawn' world.
Well, you could write a fanfiction where the reader is a spirit - like being that only Yona can see. This being gives Yona advice and support in her toughest times. Or perhaps the reader is a lost warrior who has forgotten their past, and Yona's group helps them regain their memories while they, in turn, help the group with their combat skills.
A third plot idea could be to focus on the bond between the dragons and Yona from the dragons' perspective. What do they really think of her? Do they have any doubts about following her at times? This could create some internal conflict within the group. You could also explore how their bond might change or grow stronger over time, especially in the face of new challenges that test their loyalty to each other.
Maybe a male OC who is a healer. He joins Yona's group and uses his unique healing abilities to help the team in various situations. He also has a crush on one of the female characters in the group, which adds some romantic sub - plot.
First, decide on the role of the reader in the story. Are they a friend, a helper, or something more? Then, think about the setting. Will it be in one of the existing locations in the 'Yona of the Dawn' world or a new place? After that, just start writing the first encounter between the reader and Yona or her group. For example, you could start with the reader saving one of Yona's friends from a dangerous situation.
A fanfiction could be set in a parallel universe where Zeno and Shin - ah are the main characters instead of Yona. They could be on a mission to find a cure for Shin - ah's dragon powers that are slowly consuming him. Zeno, with his immortality, would stop at nothing to save his friend.
One common theme is adventure. Since the original story has a lot of adventure elements, fanfics often continue this. Yona and Hak go on quests together, facing enemies and exploring new lands, which strengthens their bond.
One popular 'Yona of the Dawn Yona x Hak fanfic' is 'The Journey Ahead' which beautifully explores their relationship as they face various challenges together. It has great character development and a lot of sweet moments between Yona and Hak.
Some fanfics also explore the idea of a 'what if' scenario where Hak didn't grow up with Yona. How would they meet and fall in love in a completely different context? This allows for a lot of creative storytelling as the writers can re - imagine their first encounters and the development of their relationship from scratch.
Another interesting crossover could be with 'Sailor Moon'. The Sailor Scouts could join forces with Yona's gang. Yona could learn about the power of friendship and magic from the Scouts, and they could work together to protect both their worlds from a new, menacing threat.
One more theme could be the exploration of the fantasy world. Writers might create new areas in the 'yona of the dawn' world, or expand on the magic and mythology that already exists in the original story. This can make for some really interesting and imaginative fanfictions.
One popular theme is character interactions. For example, crossovers might explore how Yona would interact with characters from other fantasy worlds. Another theme could be the adaptation of Yona's journey in different settings. Maybe she finds herself in a modern world or a different historical era. Also, power combinations can be an interesting theme. If she crosses over with characters who have different powers, how would they combine or clash?