Perhaps a plotline where the Black Dragon Emperor has to form alliances in a world that is both fearful and envious of his power. He could encounter different races and factions, each with their own motives for allying or opposing him.
In some fanfictions, the Black Dragon Emperor might have a special relationship with Harry Potter himself. It could be a mentor - like relationship, teaching Harry some ancient and powerful magic that was long forgotten in the wizarding world. This would give Harry an edge in his battles against the forces of evil and also introduce a whole new aspect of magic to the story.
Well, one interesting plotline could be the silver dragon's journey to find its true home. Maybe it got separated from its family at a young age and has to face many challenges while searching for its place in the world.
One interesting plotline could be the dragon of light's journey to discover its true powers. Maybe it starts off weak but as the story progresses, it unlocks new abilities through various challenges.
One interesting plotline could be the exploration of different magic systems in the 'coiling dragon' universe that are not fully explored in the original work. For example, how certain characters develop unique spells based on their individual talents.
One idea could be the Black Dragon Emperor's powers influencing Naruto's ninjutsu in unique ways. For example, his fire - based jutsus might gain a more dragon - like quality, like the flames taking on a blackish hue and having a more destructive force.
One interesting plotline could be the main character's journey to discover their true heritage within the world of 'the black heir fanfiction'. They might face challenges and make new alliances along the way.
Another plotline might involve the dragon slayers teaming up against an ancient evil that threatens the entire world of magic. They would have to combine their unique dragon - slaying abilities to defeat it, like Natsu's fire - based attacks with other slayers' powers.
Well, a plotline might involve Luffy being trained in stealth and strategic planning by Dragon. This would add a new dimension to his character as he usually just charges head - first. Also, there could be a story where Luffy has to keep his relationship with Dragon a secret from his crew at first, and the internal struggle he faces about that.
Perhaps a plot where a dragon rider is from a different dimension and has to adapt to the world of RWBY. They could bring unique skills and knowledge that help the RWBY gang in their battles and also learn a lot from them in return. This could involve cultural exchanges as well as combat strategies.
One interesting plotline could be the restoration of the Targaryen dynasty in a more just and prosperous way. Maybe the dragonriders use their power to end feudal oppression. Another could be the discovery of new dragon eggs and the training of new dragonriders, which would bring a new dynamic to the story.