One idea could be a story where Naruto discovers a new, hidden aspect of his shadow powers that allows him to communicate with the shadows of the past ninjas. He could learn ancient techniques from them and use this knowledge to defeat a powerful new enemy.
A really cool plot could be that Naruto's shadow powers get combined with a strange new jutsu he encounters. This fusion creates a whole new set of abilities. He could then use these combined powers to save his friends from a dangerous situation, like being trapped in a genjutsu - filled maze where only his unique shadow - jutsu combination can break the illusions.
A plot idea could be that a new character with smoke powers emerges and is initially feared because people don't understand their abilities. But as the story progresses, they use their powers for good, like rescuing villagers from fires by using the smoke to absorb the heat.
One idea could be exploring a different backstory for Alina. Maybe she was born with her powers but had to hide them in a more complex way than in the original story. Another could be a fanfic where Mal and Alina's relationship develops in a parallel universe where the Darkling never existed. This would change the dynamic of their love and how they face the challenges in Ravka.
An interesting plot idea for Naruto fanfic might be to focus on the life of a minor character. For instance, what if we told the story of a genin who never made it to be a chunin but still had a significant impact on the village in some other way? Or a story where all the ninja abilities are suddenly switched among the characters, and they have to adapt to these new powers while still facing their usual enemies. This could lead to some really fun and unexpected character interactions.
One interesting plot could be a character with shadow release power being able to manipulate the shadows of ancient beasts. This would create a whole new level of challenges and adventures as they try to control these powerful and unpredictable forces.
One idea could be exploring an alternate timeline where the main characters have different allegiances. For example, Sasuke could side with Orochimaru permanently and Naruto has to find a way to bring him back without fighting. Another could be a story where the Akatsuki are actually working for a greater good that was misinterpreted, and Naruto teams up with them to fight a common enemy.
One interesting plot idea could be Naruto using his shadow clones to time - travel back to the era of the First Hokage. He could then use his modern - day knowledge and shadow clone jutsu to help shape the early history of the Hidden Leaf Village.
One idea could be that as a girl, Shadow has to face different challenges in a male - dominated Sonic world. Maybe she has to prove herself constantly to be accepted as a strong fighter.
One idea could be that Silver and Shadow are forced to team up to stop a new, powerful enemy that threatens their world. They start off distrusting each other but as they face challenges together, they begin to understand and respect one another.
Well, a great plot could be centered around a mystery. Let's say there are strange occurrences in their world that seem to be related to Bakugan Shadow's past. Mylene becomes determined to solve this mystery. As they dig deeper, they uncover secrets that not only change their understanding of Bakugan Shadow but also put them in danger. They might have to face off against an ancient enemy who is trying to keep these secrets buried. Mylene uses her intelligence and courage, while Bakugan Shadow uses its strength and special powers to overcome the obstacles in their path.
Another plot could be that Naruto is possessed by a dark spirit that gives him incredible power but also makes him do evil things against his will. His friends initially think he has turned bad, but Sakura, being a medical ninja, discovers that something is wrong. They then embark on a journey to exorcise the spirit. Along the way, Naruto has to constantly fight against the spirit's control, which could lead to some intense battles and emotional moments as he tries not to hurt his friends.