Well, it could start with Elton Castee being in his backyard. He's unaware that a black widow has made a home near his shed. As he reaches for something, the black widow bites him. This could set off a chain of events. He might first try to identify the spider to know how serious the bite is. Then, he could be faced with symptoms like nausea, sweating, and difficulty breathing. His journey from getting bitten to seeking proper medical attention or trying home remedies could be the main focus of the fanfiction.
His friends could help him. They might drive him to the hospital or call for medical assistance. They could also stay by his side, trying to keep him calm and comfortable while waiting for help to arrive.
She might be kidnapped by a supervillain who wants to use her skills for his own evil plans. For example, he could force her to break into a highly secure facility to steal some dangerous weapon or technology.
One possible plot could be that Black Widow, while on a mission, gets hit by some sort of experimental weapon or magic spell that reverts her to a child. She then has to rely on her Avengers teammates to protect her while they search for a way to reverse the effect. Her skills as a child would be limited, but her intelligence might still be intact, leading to some interesting situations where she tries to communicate complex ideas in a child's body.
It could be a rival spy agency. They might want to get information from her about S.H.I.E.L.D. and its operations. They would see her as a valuable source of intelligence.
Well, perhaps there is a plot where a powerful artifact has the ability to merge different universes. Naruto's and Black Widow's worlds start to blend. They are brought together by this strange phenomenon. At first, they are suspicious of each other. But as they discover that they are both after the same goal, which is to stop the artifact from causing more chaos and destruction, they start to cooperate. Their combined skills of ninjutsu and spycraft prove to be a formidable force against the various threats that emerge during this strange event.
One possible plot could be that in an alternate universe, Loki and Black Widow have a mission together. During this time, they develop unexpected feelings for each other. Then, Black Widow discovers she is pregnant. This leads to a whole series of events where they have to deal with both their relationship and the challenges of having a baby in a world full of danger and intrigue.
One plot idea could be that Hermione, being the intelligent and resourceful witch she is, gets inspired by Black Widow's combat skills. She might start training in a more physical and combat - oriented way, perhaps even creating her own spells that mimic Black Widow's moves. For example, she could develop a spell that allows her to move as stealthily as Black Widow. Then, she could use these new skills to protect Hogwarts during a new threat, something that the normal magical defenses can't handle alone.
The plot might involve Black Widow being sent on a mission to investigate some strange happenings that turn out to be related to the magic and mythology of Percy Jackson's world. Percy gets involved because he has knowledge of these things. They start off at odds but as they uncover the mystery together, they start to respect and rely on each other. Their different backgrounds - Percy from a world of gods and monsters and Black Widow from a world of superheroes and villains - would create a lot of room for interesting character development and plot twists.
One possibility could be that Thanos captures Black Widow to use her as bait for the other Avengers. He might think that her comrades will come to her rescue and he can then ambush them all at once.
One possible plot could be that Harry Potter, as the son of Black Widow, discovers his mother's secret past in the wizarding world. He might inherit some of her unique skills, like her combat abilities, and use them to face new threats in Hogwarts. Maybe he forms a special group of friends who are intrigued by his strange heritage and they all embark on adventures together.