Perhaps the plot could revolve around a prophecy that involves the dragon of darkness. The story might show how different factions react to this prophecy, some trying to fulfill it and others trying to prevent it. It could also be that the dragon of darkness is actually a misunderstood creature, and the story is about it finding acceptance among other beings in the fictional world. There could be a plotline where the dragon is the key to unlocking a great power, but it's a power that could either save or destroy the world depending on how it's used.
One possible plotline could be the dragon of darkness being hunted by a group of adventurers who see it as a threat to their world. Another could be the dragon trying to find a way to overcome its own dark nature.
A plotline could be that the dragon of darkness is an ancient being that has been asleep for centuries and wakes up to find a world that has changed. It then has to navigate this new world while dealing with its own powers and the fear that it instills in others. Or, the fanfiction could tell a story of a young character who befriends the dragon of darkness and together they go on a journey to right the wrongs in the fictional realm, facing many obstacles along the way due to the dragon's dark reputation.
A possible plotline could be the discovery of an ancient power related to darkness and flame that threatens the balance of the Naruto world. Naruto and his friends then have to find a way to either control it or destroy it.
One possible plotline could be that Naruto is constantly ostracized by the village, which slowly breaks his spirit and makes him turn to the dark side. He might start to use forbidden jutsus without any moral restraint.
One possible plotline could be that Harry, as a submissive dragon, is forced to follow the commands of a more powerful dragon or wizard. He might struggle against this submissive role and try to break free.
One possible plotline could be that the gold dragon is a mythical creature that Naruto discovers during one of his missions. He then has to figure out how to communicate with it and gain its trust.
One plotline could be a quest to find the Dragon Mask. The characters might have to go through various challenges and obstacles in different parts of the TF world to locate it.
A possible plotline could be that the dragon is lost and Harry helps it find its way home. Along the way, they form a bond and the dragon becomes Harry's ally. Harry could use the dragon's abilities, like flying on its back, to gain an advantage in his fight against the forces of evil.
One possible plotline could be a character's accidental transformation. For instance, a young character exploring an ancient ruin stumbles upon a magical artifact or spell that causes them to transform into a dragon. This then sets them on a journey to find a way to reverse it or to use their new form for good.
Perhaps the dragon in Jon's fanfiction is the last of its kind, and Jon has to protect it from those who want to harm it. There could be a whole story of them hiding, fighting off hunters, and trying to find a new place for the dragon to live safely.
One possible plotline is that the dragon helps Harry discover a hidden magical place. Since dragons have a strong sense of magic, it could lead Harry to a place full of ancient spells or powerful artifacts.
Perhaps there is a plotline where the main character discovers the source of their inborn darkness. It could be related to a family secret or a past event that has been hidden from them. As they uncover the truth, they have to deal with the consequences and decide whether to continue down the path of darkness or strive for a different future. This discovery could also impact their relationships with other characters in the fanfic, causing some to turn against them while others offer support.