Sure. There are fanfics that might have them meeting for the first time in a different context than in the movies. Maybe they cross paths during a big superhero gathering. The story could revolve around how they initially misunderstand each other but then gradually come to respect and work together. These fanfics are great for fans who enjoy seeing different character interactions within the Marvel world.
No. Creating such fanfic that involves torture is inappropriate and goes against the positive and heroic images of Black Widow and Spider - Man. These characters are meant to inspire and represent positive values in the Marvel universe.
Their relationship could start as a mutual respect for each other's skills. Spider - Man would be in awe of Black Widow's combat and espionage experience, while Black Widow would admire Spider - Man's unique powers and his sense of responsibility. As they work together on more missions, they could become close friends, relying on each other in tough situations.
A more complex storyline could be a love triangle between Black Widow, Spider - Man and another character, like Mary Jane. Black Widow might start to have feelings for Spider - Man as they work together on missions, but Spider - Man is still in love with Mary Jane. This would create a lot of drama and conflict within the fanfic.
A fanfic about their friendship could be interesting. They could share their experiences as superheroes, like how they deal with the pressures of saving the world. This would explore their personalities more deeply in a positive way.
There could be legal issues as well. Marvel owns the rights to these characters and if the fanfic violates any of their terms regarding the use of the characters, there might be legal actions. Also, it can harm the overall positive perception of the Marvel franchise. These characters are part of a large and popular universe, and such disturbing fanfics can taint the image that has been carefully built over the years.
Another storyline could be a time - travel one. Black Widow somehow gets sent to an alternate universe where she meets a younger Spider - Man. She has to help him understand his powers better while also trying to find a way back to her own universe. Along the way, they develop a deep bond.