Perhaps in the fanfiction, Natasha as a kid gets caught in a magical mishap that gives her unique powers. The Avengers then have to figure out how to control these powers while also protecting her from those who would use her new abilities for evil. She might struggle with the changes in herself and how the other Avengers see her now that she's different.
A plot could revolve around a kid Natasha joining the Avengers on a time - traveling adventure. They go back in time to stop an event that could change the future of the Avengers. Along the way, Natasha has to use her wits and natural skills to overcome various obstacles, and she forms a special bond with the other Avengers members during this journey.
To develop kid Natasha, you could focus on her backstory. Maybe she was an orphan and had to learn to fend for herself at a young age. This would make her resourceful and street - smart.
One plot idea could be Natasha and Steve having to go undercover together during a mission related to Ultron's early schemes. They could pretend to be a couple, which would lead to some awkward yet heartwarming moments as they navigate their feelings while also trying to stop Ultron. Another idea is that Natasha discovers a hidden past of Steve that is somehow connected to the creation of Ultron and they have to deal with the revelations together.
One idea could be that Naruto is somehow transported to the Marvel universe and meets Natasha Romanoff. They could team up to fight a common enemy that has powers similar to those Naruto has faced in his own world, like a villain with the ability to control shadow clones.
She could be a super - spy too, but on a different side initially. Maybe she was brainwashed by a shadowy organization. Natasha then has to fight her sister while also trying to bring her back to her senses. It would be a story full of action and emotional turmoil.
A really cool plot idea could be that the Avengers are watching Endgame in a sort of 'alternate reality cinema' where the events in the movie start to bleed into their real world. So they have to stop the movie from fully playing out to prevent chaos in their own universe. This would involve a lot of action and strategic thinking as they try to stop things like Thanos from emerging from the screen while also trying to understand the significance of what they're seeing in the movie.
One idea could be that the mutants and the Avengers have to team up against a common enemy that is immune to their individual powers. So they must learn to combine their abilities in new ways. For example, Wolverine's healing factor could be used to keep an injured Avenger alive during a long battle while Iron Man figures out a way to defeat the enemy.
One idea could be that Harry Potter is magically transported to the Avengers' universe. He could use his magic to help the Avengers in battles, like creating protective shields with spells. Another idea is that the Avengers are somehow sent to Hogwarts, and they have to learn about magic while also dealing with threats in the wizarding world. For example, Iron Man might try to figure out how to integrate his technology with magic.
One idea could be exploring the family dynamics when the Avengers have to take care of a young superhero in training. It would be fun to see how they each contribute to the kid's growth, like Tony Stark teaching about technology and Captain America instilling values.
One idea could be the Avengers facing off against a new, powerful villain who has the ability to turn their own powers against them. This would lead to some really intense battles and strategic thinking on the Avengers' part.
One idea could be that the adopted character has a special power that the Avengers initially don't understand. This power could be something like the ability to communicate with animals, which helps them during a mission where they need to track a villain through a forest. Another could be that the character has a connection to an ancient artifact that the Avengers are also interested in for some reason, and this connection leads to a series of adventures.