A great storyline could be about M'gann learning about the ninja arts from Naruto, especially those related to Amaterasu. Maybe Naruto is on a mission in M'gann's universe and has to use Amaterasu to defeat a powerful foe. M'gann then becomes interested in this strange power and wants to learn more. There could also be a story where an evil version of Naruto uses Amaterasu against M'gann, and she has to find a way to stop him using her own unique abilities.
One possible storyline could be a crossover where Naruto and M'gann are brought together in a strange new world. Amaterasu could be the key to getting them back to their respective universes. For example, they might have to find the origin of Amaterasu's power in this new world to unlock a portal. Another storyline could be that M'gann is captured by an enemy who wants to study Amaterasu's power, and Naruto has to rescue her.
Naruto, with his experience in combat and using various jutsus like Amaterasu, can bring a new dynamic to the story when paired with M'gann. Amaterasu, being the black flames, can be written as a tool for Naruto to protect M'gann in some fanfictions. M'gann, on the other hand, could offer Naruto a different perspective on power and morality. The fanfiction might explore how they grow together as characters while dealing with the implications of Amaterasu's existence in their shared adventures.
One great storyline could be Naruto somehow gaining the power of Amaterasu. He might struggle to control it at first, just like Sasuke did. It could lead to him having to train in secret to master this new and dangerous ability. Another idea is that Amaterasu is used as a weapon against a powerful new enemy that Naruto has to face. The fanfiction could explore how Naruto uses his quick thinking and ninja skills to counter the destructive force of Amaterasu.
One storyline could be that the British mage is accidentally transported to the Naruto world. They then have to find a way to get back home while also dealing with the various threats in the Naruto universe. Along the way, they could make friends with Naruto and his friends and use their magic to help in battles against the Akatsuki.
One possible storyline could be about a new threat emerging in the ninja world that only the combined powers of Naruto, Fem Kyuubi, and Fem Amaterasu can defeat. They have to learn to work together quickly, despite their differences. Another could be a story where Fem Amaterasu is from a different dimension and Fem Kyuubi has to help Naruto understand her powers to send her back home. And at the same time, they form a strong bond during the process.
A storyline could be that Hypno senses the unease of a pregnant Pokémon due to changes in its environment. Hypno then uses its powers to create an illusionary safe haven for the Pokémon to relax. It's a simple yet heartwarming concept for a fanfiction.
One possible storyline could be that Naruto is somehow transported to the Young Justice universe and meets Black Canary. They initially have a misunderstanding due to their different backgrounds, but then they realize they have a common enemy. Another storyline could be that Black Canary is investigating a strange phenomenon and discovers Naruto's world. She teams up with Naruto to solve a problem that affects both their worlds. Maybe a powerful villain is trying to merge their two universes in a chaotic way, and they have to stop it.
One possible storyline could be that the Zanpakuto with Amaterasu's power is a gift from an ancient shinobi to Naruto. Naruto then has to learn to control this new and extremely powerful weapon. He might face challenges like accidentally using it against his friends in the beginning due to its overwhelming power.
One possible storyline could be that Venom is lured to Earth by a powerful villain who wants to use Venom to take on the Avengers. But Venom realizes he's being used and teams up with the Avengers to take down the real villain.
One possible plot could be that Naruto, in his godlike state, somehow ends up in the same universe as M'gann M'orzz. They initially clash due to their different upbringings and powers. Naruto's determination and M'gann's empathetic nature gradually bring them together. They start to understand each other's worlds and find common ground in their desire to protect those they care about. As they train together, their relationship deepens into a romantic one.
One storyline could be a competition. For example, a race or a mission where Anakin and his rival are pitted against each other to see who can achieve a goal first. This could create a lot of tension and show different aspects of their characters.