One idea could be that they are on a secret mission together. The Winter Soldier's past memories start to resurface during the mission, and Black Widow helps him deal with the confusion and the emotional turmoil. They gradually develop a deeper connection as they rely on each other's skills.
A plot could revolve around Black Widow and Winter Soldier having to protect a young mutant who has the power to expose a global conspiracy. Their different skills and experiences would come into play as they face various threats. In this fanfiction, they might also develop a deeper understanding of each other's traumas along the way.
One interesting fanfiction could be about their secret missions together before the events of the main movies. They might have to infiltrate a high - security enemy base where they rely on each other's unique skills. The Winter Soldier's combat expertise and the Black Widow's espionage skills would make for a great combination.
One plot idea could be that the Winter Soldier is on a mission and accidentally crosses paths with She - Hulk. She - Hulk initially mistakes him for a threat but then realizes he's more complex. They end up having to team up to take down a common enemy, like a new super - powered criminal organization that's causing chaos in the city.
One idea could be a story where Loki and Black Widow are forced to team up on a mission in a parallel universe. They have to overcome their initial distrust of each other due to their different backgrounds and allegiances.
One idea could be that they team up on a dangerous mission in a post - apocalyptic world. Their different skills, Black Widow's combat and espionage expertise and Quake's seismic powers, would make for an exciting dynamic as they fight off various threats.
Another plot could involve a time - travel scenario. Spiderman and Black Widow get sent back in time to a crucial moment in the history of the Avengers. They have to work together to make sure the events unfold correctly without changing too much of the timeline. Along the way, they discover secrets about their predecessors and how they can apply those lessons to their own lives.
One popular trope is the 'partners in danger' where they face various threats together. For example, in many fanfictions, they are on a mission against a powerful new enemy that the Avengers haven't encountered before. Another is the 'slow - burn romance' trope. Since both characters have complex pasts and are a bit guarded, a slow - developing relationship between them can be very engaging. It might start with just a mutual respect for each other's skills and gradually turn into something deeper as they understand each other better.
One idea could be a story where Falcon and Winter Soldier have to team up with an unexpected ally from their past. Maybe an old enemy who has a change of heart and holds the key to stopping a new threat.
Another interesting plot could be centered around a new threat that specifically targets Sam and Bucky because of their connection to Captain America. This threat could be a powerful and mysterious organization that has been observing them from the shadows. The story could focus on how they uncover the motives of this organization and fight back.
One idea could be a crossover with the X - Men. The Winter Soldier could be sent on a mission to retrieve a mutant who has some sort of power that could be dangerous in the wrong hands. He then has to face off against some of the X - Men who are protecting the mutant. Another plot could involve a crossover with Doctor Strange. Maybe the Winter Soldier gets caught in a magical spell that makes him relive some of his past traumas in a different way, and Strange has to help him break free. A third plot could be a crossover with the Guardians of the Galaxy. The Winter Soldier is somehow transported to space and has to team up with the Guardians to get back to Earth while also dealing with some intergalactic threats.