You could write a fanfiction where Gajeel enters Dragon Force during a major battle against a powerful dark guild. In this story, his transformation could turn the tide of the battle and inspire his comrades. He could also have some internal struggle during the transformation, like dealing with the overwhelming power and the fear of losing control.
Another interesting plot could be a story where Gajeel discovers a new aspect of his Dragon Force. Maybe he realizes that he can communicate with dragons in a different way while in this form. This could lead to a quest to find out more about his dragon heritage and uncover secrets that were long forgotten.
One interesting plot idea could be that Gajeel discovers a new type of dragon magic that only Levy can help him understand. Maybe it's a magic that involves ancient dragon runes, and Levy's knowledge of books and languages is crucial in deciphering it. As they explore this new magic together, their relationship deepens.
One plot idea could be that Levy, as the princess, has a secret power that only Gajeel, the dragon, can help her control. As they interact, they start to develop feelings for each other. Another could be that Levy is kidnapped by an evil force and Gajeel, being the powerful dragon, goes on a dangerous quest to rescue her, during which they discover a long - lost prophecy about their fates.
A crossover with the Avatar: The Last Airbender world would be cool too. Gajeel could be a metalbender from a far - off land. He could interact with Aang and the gang, and his skills could be both a help and a hindrance in their quest to save the world. For example, his metalbending might be useful in building structures but could also cause trouble if misused.
First, you need to know the character well. Read the original manga or watch the anime to understand Gajeel's personality, his relationships, and how his Dragon Force is presented. Then, come up with a simple idea, like a situation where he has to use his Dragon Force in an unexpected way.
A plot could involve Wendy using her Dragon Force to protect the Fairy Tail guild from a powerful dark magic user. She has to learn to control and enhance her Dragon Force abilities during the battle to save her friends. This could include her having to face her own fears and doubts about her power. For example, she might initially be afraid that she's not strong enough, but as the battle progresses, she realizes the true potential of her Dragon Force and how it's not just about raw power, but also about her connection to the dragons and her friends at Fairy Tail. In the end, she could defeat the dark magic user and become more confident in her abilities.
One idea could be exploring the backstory of Rey's parents in more detail. Maybe they were part of a secret Jedi order that was in hiding. Another could be a story about Finn's life before he defected from the First Order, like his training and relationships with other stormtroopers. Also, a fanfiction could focus on Kylo Ren's struggle with the light side of the Force that he tries to suppress.
You could also write about Naruto forming a special force within the Hidden Leaf Village. This force would consist of some of the most talented ninja from different clans. They would be trained by Naruto himself to face threats that are beyond the capabilities of the regular ninja forces. It could explore how Naruto's leadership skills and his understanding of different ninja abilities would help in creating a formidable team.
You could write a fanfiction that delves deeper into the relationship between Arthur and Shinra. Maybe they get into a big argument over their different approaches to being a hero. Shinra believes in using his powers for the greater good in a more practical way, while Arthur is all about living out his 'knight in shining armor' fantasy. This argument could lead to them going their separate ways for a while, and then having to come back together to face a powerful Infernal that neither of them could defeat alone.
One idea could be exploring an alternate universe where the Battle Force 5 team has different powers or vehicles. For example, instead of their regular rides, they could have flying saucers with unique offensive capabilities.
One idea could be a story where the heroes from different Jump universes have to team up against a new, unknown threat that is slowly corrupting their worlds. Another could be a character - driven story focusing on a minor character from one of the Jump series and their journey through the chaotic world of Jump Force.