Well, a lot of fanfiction might focus on creating alternate endings for Black Widow. For instance, instead of her sacrifice in 'Avengers: Endgame', she could have found a way to survive and continue her journey as a hero. Another concept could be crossovers, like Black Widow teaming up with characters from other Marvel universes.
Another concept might be the psychological aspect. How does she adjust to being a giantess? Does it change her self - perception? Maybe she has to deal with feelings of isolation as she is now so different from others. Also, her relationships with her teammates like the Avengers could be greatly affected.
One interesting concept could be how the symbiote enhances Black Widow's combat skills. It might give her super strength and agility, allowing her to take on more powerful foes. For example, she could use the symbiote's tendrils to grapple enemies from a distance or quickly scale buildings during a chase.
One concept could be a story where Black Widow is somehow transported into the Harry Potter universe. Maybe she has to use her combat skills and spy training to navigate Hogwarts and deal with the Dark Arts. For example, she could be an undercover agent sent to figure out Voldemort's plans and ends up teaming up with Harry and his friends.
I'm not sure about specific titles off the top of my head, but you can start by looking on fanfiction.net. There are usually a lot of stories there. Just search for 'Black Widow Program' and you'll find a bunch. Some might be about her origin story, others could be action - packed adventures set in the Marvel universe.
One interesting storyline could be a mission where Black Panther and Black Widow have to team up to take down a powerful international arms dealer. They could combine their unique skills, with Black Panther's enhanced strength and agility from the heart - shaped herb and Black Widow's spy training and combat expertise. Another could be a story set in Wakanda where Black Widow is sent on a diplomatic mission and she and Black Panther develop a mutual respect and friendship as they deal with political intrigue within Wakanda and threats from outside forces.
One interesting concept could be the use of magical spells for unique purposes. For example, in some black magic fanfiction, spells are used to communicate with otherworldly beings that normal magic can't reach. This adds an element of mystery and danger.
In 'the black eon fanfiction', perhaps the power dynamics are really engaging. There might be characters with extraordinary powers and how they interact with others who have different levels of power. Also, the plot twists could be a great concept. It could keep readers on their toes as the story unfolds in unexpected ways.
One interesting concept could be the exploration of unique powers. In black torch fanfiction, characters might possess powers that are different from the original source, like the ability to control shadows in a more complex way. Another could be the development of relationships. For example, characters that were just acquaintances in the original might form deep friendships or rivalries in the fanfiction.
One interesting concept could be new alien species. Maybe a species that has the ability to shapeshift into any human form and they use this to infiltrate the Men in Black organization. It would create a lot of mystery and action as the agents try to figure out who is real and who is an alien impostor.
A third concept could be the Black Joker's moral compass. Fanfiction could explore whether he is truly evil or if there are certain things that could make him question his actions and motives, perhaps through interactions with other characters that force him to re - evaluate himself.