Well, perhaps Merlin discovers a hidden magic that starts to transform him into a dragon. He might struggle with his new form, trying to control his dragon instincts like the urge to hoard treasure or fly away to a secluded lair.
It could be Morgana. She might see Merlin's transformation into a dragon as a threat to her own power and plans. So, she tries to stop him from fully becoming a dragon or tries to use his new form for her own evil purposes.
Well, it could be about Kobayashi suddenly finding herself in a situation where she starts to transform into a dragon. Maybe it's due to a magic spell gone wrong. She then has to deal with newfound powers and instincts.
Well, perhaps the story could start with Natsu having a strange encounter that begins his transformation into a dragon. Maybe he discovers some ancient magic or a hidden power within himself that is related to dragons.
Well, one possibility is that Merlin uses his magic secretly to gain the support of the people. He might perform great feats during times of crisis, like saving the kingdom from a powerful enemy. And then, through a series of events, the nobles and commoners alike start to see him as a true leader and he is finally crowned king.
Maybe it could involve Natsu having to go through some really tough trials to prove himself worthy of becoming the Fire Dragon King. For example, he might have to battle powerful enemies that are related to the dragon world's ancient secrets.
In a 'Fairy Tail Lucy becomes a Dragon Slayer' fanfic, it could start with Lucy being in a life - threatening situation. To survive, she unknowingly absorbs the power of a dying dragon. This power starts to change her. At first, she is scared of the changes. But then, with the support of her friends, she decides to embrace it. She then begins a journey to master her new powers. She might learn that her Dragon Slayer magic is linked to a special type of celestial spirit that has dragon - like qualities, and she has to find and bond with this spirit to fully control her powers.
Well, it could be that Hiccup is cursed by an evil sorcerer who wants to turn him into a dragon as a form of punishment. But as he turns into a dragon, he finds that he has a new connection with the dragon world. He starts to see things from a dragon's perspective and uses this to bring peace between humans and dragons in a whole new way.
Maybe Natsu discovers a new magic spell that accidentally turns him into a dragon. He then has to figure out how to reverse it while dealing with the new powers and instincts.
Well, perhaps Hedwig could be magically transformed into a dragon. Then she might go on adventures, using her new dragon abilities like flying faster and breathing fire to protect her wizard friend from dark forces.
Another idea is that a villain creates a rift between the two universes. The Avengers and Merlin have to team up to close this rift. During their journey, they exchange skills and knowledge. Black Widow could teach Merlin some combat skills, while Merlin could show the Avengers how to use magic in a more strategic way. This way, they not only close the rift but also become stronger as a combined force.