One idea could be exploring the backstory of the main character's magical powers in more depth. Maybe she discovers a hidden origin of her powers that changes her perception of herself.
Another plot could involve a new character entering the story, a mysterious traveler who has knowledge about an ancient prophecy related to the Girl of Fire and Thorns. This new character could either help or hinder the protagonist on her journey. For example, they could initially seem helpful but later be revealed to have their own motives that conflict with the main character's goals.
One idea could be exploring a different origin for the main characters. For example, what if Feyre was from a long - lost clan in the mortal world with unique powers? Another could be a 'what if' scenario where Tamlin didn't make the mistakes he did in the original story and he and Feyre had a more harmonious relationship. Or perhaps a story where the Night Court has to face a new, unexpected threat that forces them to form alliances with old enemies.
One idea could be exploring the backstory of a minor character in more detail. For example, a character who only had a brief appearance in the original but has a really interesting family history or a hidden power that could be developed in the fanfic.
One idea could be exploring a different path for the main character's relationship with a key figure. For example, instead of the initial enmity, they could start as reluctant allies from the very beginning. Another plot could involve a new magical threat that the characters have to face together, something that wasn't in the original story.
One idea could be that Fire Boy and Water Girl find a magical forest where the rules of their elements are reversed. Fire Boy has to be careful not to extinguish himself in the overly wet areas, and Water Girl has to avoid drying up in the super - hot spots. They have to work together to find a way out of this strange forest.
One idea could be exploring the backstories of minor characters in more depth. For example, the soldiers who follow the main characters often have their own motives and lives that could be fleshed out.
One idea could be that a dragon is reincarnated into a different tribe and has to adapt to their new way of life while also carrying memories of their past life. For example, a SeaWing reincarnated as a SandWing would struggle with the arid climate and different social norms.
One idea could be a Fairie's journey to discover her hidden powers. Maybe she stumbles upon an ancient relic that unlocks new abilities within her.
One idea could be Peacemaker growing up and having to face a new threat to the dragon tribes that no one expected. Maybe it's a mysterious illness that only he can find a cure for because of his unique upbringing. Another plot could involve Peacemaker making unexpected friendships with dragons from tribes that have been historically at odds, and through their bond, they work towards greater unity among the tribes.
Well, in 'naruto rainbow fire fanfiction', a cool plot might be that the rainbow fire is actually a key to a different dimension. Naruto, being the curious and brave ninja he is, accidentally stumbles upon this while on a mission. He then has to figure out how to use the rainbow fire to get back to his own world, all while facing strange creatures and new forms of chakra in this other dimension. Also, the rainbow fire could be related to a prophecy that only Naruto can fulfill, which sets him on a grand adventure.
One idea could be a story that focuses on the backstories of the minor characters. For example, exploring the life of a random student from one of the houses before they entered the academy. It could show their family, their dreams, and how they ended up at the academy.