One common theme is the clash and subsequent integration of two very different worlds. Harry Potter's magical world and the high - tech, superhero - filled world of Marvel. Another theme is redemption. Bucky Barnes is often on a journey of self - redemption, and Fem Harry Potter, with her own experiences of fighting against dark forces, can play a role in that journey.
The fact that Bucky is Tony's father in this fanfic would have a huge impact on Tony's character development. Tony might be more empathetic towards Bucky's situation as a victim of Hydra. Bucky could have taught Tony about his past, including the history of Hydra and the super - soldier serum. This knowledge could have made Tony more cautious in his dealings with the military and other powerful organizations. It could also lead to a different kind of Iron Man suit, perhaps one that was more focused on stealth and infiltration, skills that Bucky would have been familiar with.
Well, if Natasha and Bucky were Peter's parents in fanfiction, it would completely shift Peter's backstory. For one, he might inherit different skills. Since Natasha is a master spy and assassin, Peter could have a natural inclination towards stealth and intelligence - gathering. Bucky, with his super - soldier strength and combat skills, could pass on enhanced physical abilities to Peter. His origin story might not be about being bitten by a radioactive spider but something more related to the super - soldier serum or some secret spy training. It could also change his relationships. His interactions with the Avengers would be different as he'd be more closely related to two of their members.
One popular piece might be 'The Unlikely Alliance'. It weaves a story where Fem Harry Potter and Bucky Barnes find themselves in a situation where they have to team up against a common magical - technological threat. Their different worlds collide in an interesting way, with Harry's magic and Bucky's combat skills complementing each other.