Well, it's not super common but it does exist. There are different reasons for this kind of plot. Maybe the writer wants to explore the consequences of a breakdown in their relationship. They had their differences in the movies, like in 'Civil War', and some fanfic writers take it to an extreme by having Tony kill Steve to show how far things can go wrong when they can't resolve their issues.
One great Steve Tony Avengers Assemble fanfiction is 'The Road to Redemption'. It focuses on Steve and Tony's complex relationship as they lead the Avengers. The story has amazing character development and some really exciting action scenes.
The theme of sacrifice is also quite common. They are often put in situations where they have to sacrifice something for the greater good or for each other. For example, in some fanfics, Steve might sacrifice his own safety to protect Tony or vice versa. And a lot of fanfics also explore the theme of trust. They start with a lack of trust due to their different personalities and views, but as the story progresses, they learn to trust each other more.
Steve might compare Tony to Howard based on their personalities or leadership styles. Maybe he points out similarities or contrasts in their decision-making.
One reason could be to explore the extreme consequences of their ideological differences. In the official story, they had disputes over things like the Sokovia Accords. In fanfiction, this could be pushed to the limit, leading to Tony taking Steve's life.
Steve and Tony are two of the most iconic characters in the Avengers. Their relationship has been a central part of the movies. In fanfiction, writers can take this relationship in new directions. They can show more of their emotional side, their insecurities, and how they deal with the challenges of leading the Avengers. The fanfiction also often includes other beloved Avengers characters, creating a rich and engaging story. All these factors combined make Steve Tony Avengers Assemble fanfiction very popular.
I think this kind of fanfic can be quite controversial. In the Avengers universe, Steve and Tony have a complex relationship, and adding such a plot of 'cheating' with Bucky can change the whole dynamic. Some fans might like it for the drama it creates, but others might feel it goes against the original spirit of the characters' relationships.
There's also 'Steve and Tony: A New Beginning'. This fanfic takes an interesting approach where they are forced to work together in a new and unexpected situation. It has a lot of action scenes combined with their emotional interactions. It's a great read if you like to see them in challenging scenarios.
Peter Parker could be a popular character in stony Avengers Academy fanfiction. Since he's young and has a lot to learn, he can look up to Tony and Steve. He might get caught in the middle of their relationship drama sometimes, which adds some light - hearted moments. Additionally, Clint Barton can be there. His archery skills and laid - back attitude can contrast with the more intense relationship between Tony and Steve, and he can play an important role in some of the academy's adventures.