One idea could be that the OC has to deal with the legacy of Black Widow. He might struggle with living up to her name while also trying to carve out his own identity in the superhero world.
You can start by giving him some of Black Widow's traits, like her combat skills and strategic mind. But also add his own unique qualities, for example, a different moral code or a special power.
A common theme is the oc helping Black Widow overcome her past traumas. Since she has a complex backstory, the oc can be a source of support and understanding.
Another theme is the exploration of trust. Since Black Widow is a character who has trust issues, the male OC's relationship with her often delves into how they build trust. This can involve the OC proving himself worthy of her trust through various heroic deeds or by being there for her during difficult times. In some fanfictions, it can also be about Black Widow learning to trust again after past betrayals. It's a complex theme that adds depth to the stories.
Peter himself would have a different sense of self. Growing up as the son of Black Widow, he would likely be more stealthy and perhaps a bit more jaded. He might not be as naive as the regular Peter Parker, having been exposed to some of the darker aspects of the superhero world through his mother's stories or her old associates.
One idea could be exploring how Peter's spidey - sense might be affected by Black Widow's training. Since she's highly skilled in combat and espionage, she could train Peter to use his senses in more strategic ways during battles.
A possible plot could be that Spiderman discovers his true mother is Black Widow when he starts to have strange memories or abilities that he can't explain. He then embarks on a journey to find out more about his mother's past and his own origin. Along the way, he might face enemies who are after him because of his connection to Black Widow.
One common theme is friendship. The Fem OC and Black Widow often start as friends or allies. Another theme is redemption. Sometimes the Fem OC has a past she needs to overcome, and Black Widow helps with that. Love is also a big theme, as their relationship can develop into a romantic one.
Sure. You can try looking on fanfiction.net. There are often many original character (oc) paired with Black Widow stories there. Some might be about an oc being her partner in a mission, and they develop a deep bond over the course of the adventure.
First, give your OC a strong backstory. For example, if your OC was also trained in the Red Room, what made their experience different from Black Widow's? Maybe they had a mentor within the program who influenced them in a unique way.