One great storyline could be the Black Ranger having to face a new, powerful enemy alone. Maybe he gets separated from the rest of the Power Rangers and has to rely on his own ninja skills and inner strength to survive and defeat the foe. Another could be a story where the Black Ranger discovers a new power within himself that has been dormant all this time. It could be a power that has a connection to an ancient ninja legend, and he has to learn to master it while also dealing with the regular threats the Power Rangers face.
One potential ally could be an old ninja master who has been in hiding. The Black Ranger might stumble upon this master while on a solo mission, and the master decides to train him further, becoming a powerful ally in his battles. Another could be a mysterious figure who has the power to control the elements in a different way than the Rangers. They could team up with the Black Ranger to fight a common enemy that is immune to the normal Ranger powers.
One idea could be a crossover where the Naruto characters are transported to the world of Power Rangers Ninja Storm. They could team up with the Power Rangers to fight a common enemy, like an evil ninja clan that has the power to use both Naruto - style jutsu and the technology - based weapons of the Power Rangers. For example, Naruto could teach the Rangers how to better control their chakra, while the Rangers could show Naruto some cool new combat moves using their morphers.
There could be many interesting storylines in such a fanfiction. Maybe it could explore how Tori's pregnancy affects her role as a Power Ranger. For example, she might have to balance her duties with taking care of herself and the unborn child. She could also face challenges from the enemies who see her pregnancy as a weakness, but in reality, it makes her even more determined to protect the world for the future of her child.
First, you need to know both universes well. Read up on Naruto's character backstories, the different jutsu, and the world - building in that series. Do the same for Power Rangers Ninja Storm, understand their powers, the relationships between the Rangers, etc. Then, come up with an interesting plot. It could be a simple adventure where they team up, or something more complex like a mystery that involves both universes. For example, a missing ninjutsu scroll in Naruto's world that has the key to a new power for the Power Rangers. Keep the characters in - character. Naruto should act like Naruto, with his determination and his goofy side at times. The Rangers should also have their distinct personalities.
One idea could be exploring the backstories of the Ninja Storm Rangers in more depth. For example, what were their lives like before becoming Rangers? Another could be a crossover with another Power Rangers series, like how they would interact with the Dino Thunder Rangers. Maybe a story where they face a new, more powerful villain that forces them to develop new powers or strategies.
Conner, another member of the Dino Thunder team, is a great character to pair with the Green Ranger. They could have a friendly rivalry that turns into a strong friendship as they face challenges together. Their different personalities, with Conner being more impulsive and the Green Ranger perhaps more reserved, would create an interesting dynamic.
One interesting storyline could be the Green Ranger OC coming from a different dimension where the rules of power are different. They have to adjust to the new team while also bringing in their unique combat skills. For example, they might have a special way of summoning their zord that the other Rangers have never seen before.
Consider their backstory. They could be an outcast from their own planet who was found and trained by an old, retired Power Ranger. Their alien origin gives them a different perspective on things. Also, their suit design can be unique. Instead of the regular green, it could have some blue accents or different symbols that represent their individuality.
First, focus on your original character (OC). Think about their backstory, like where they come from and what their goals are. For example, if your OC is a new ninja ranger, they could be seeking revenge for a lost family member. Then, incorporate the unique elements of Ninja Storm, such as the ninja powers and the team dynamics. Maybe your OC has a power that no one else has and it causes some jealousy among the team at first. You can also introduce new villains that specifically target your OC. This creates a lot of tension and opportunities for interesting storylines.