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.
There could be a female dragon named Ignis who is very fiery and passionate, always trying to be the closest to Natsu. Another could be a more gentle dragon named Aqua, who has water - based powers and uses her calm nature to balance out the more intense dragons in the harem.
In addition to Lucy and Erza, there could be other female characters from the series. Maybe some minor characters who have always admired Natsu from afar. For example, that one girl from the guild who always blushes when Natsu is around. Another possibility is a powerful female dragon who sees Natsu's transformation into a Dragon God as a sign of his worthiness. She might join his harem, bringing a different kind of relationship dynamic as she has her own dragon - like qualities and power. And there could be a female mage from a different guild who hears about Natsu's new status and is intrigued, eventually becoming part of his harem.
Well, it could be about Natsu suddenly finding himself in a situation where he has multiple dragon companions who are all attracted to him. Maybe he has to deal with their different personalities and powers while also trying to figure out how he got into this harem situation in the first place.
Maybe an ancient dragon that has been awakened from its slumber and views Natsu as an intruder in the dragon world. Since Natsu is a new - made dragon, this old dragon might try to drive him out or even harm him.
One possible plot could be that Natsu is cursed by a dark wizard. This curse slowly transforms him into a fire dragon. As he changes, he struggles to control his new dragon - like instincts and powers. His friends initially fear him but then realize they need to help him break the curse.
Well, perhaps the plot could involve Natsu's transformation being a result of some powerful magic or a dark curse. He might struggle to control his new dragon form at first, causing chaos among his friends and allies.
In many of these fanfictions, the way Natsu's dragon form affects his relationships is a big plot point. For example, his enemies might be more afraid of him, or his friends might see him in a new light. Also, the use of his dragon form in battles against powerful villains can be really engaging. His new abilities could give him an edge in combat that he didn't have before, like breathing fire in a more powerful way or having enhanced strength and speed.
A great fanfiction to check out is 'When Natsu Became a Dragon'. This one focuses a lot on the emotional aspect of Natsu turning into a dragon. It shows his inner turmoil and how his friends react to this new side of him. There are some heart - warming moments as they all try to understand and support Natsu through this transformation.
Well, it could be about Natsu's journey to becoming a Dragon God and how he attracts a harem along the way. Maybe he gains new powers that make him irresistible to certain characters.