Well, perhaps Tony Stark time - travels during the Civil War to a moment when he first started developing Ultron. He then uses his future self's wisdom to avoid creating Ultron in the first place. This would change the entire dynamic of the Civil War as the destruction caused by Ultron was a major factor in the public's distrust of the Avengers. He could also time - travel to meet a younger version of Captain America and try to understand his point of view better from the start.
A great plot idea could be that Tony Stark time - travels to the time just before the battle in the airport during the Civil War. He could then try to secretly communicate with each Avenger individually, using his knowledge of their future actions and feelings. He might tell Black Widow about how her actions will further divide the team in the future, or he could tell Vision about the power of the Mind Stone and how it can be better used to prevent the upcoming chaos. By doing this, he hopes to stop the actual fight from happening.
One idea could be that Pepper tries to mediate between Tony and Steve during the Civil War. Since she knows Tony so well, she might be able to find common ground that others can't. Another could be Pepper getting involved in the fight herself, using her business acumen and strategic thinking to help Tony's side. Maybe she discovers a hidden plot that could change the course of the war.
One idea could be that Tony Stark's daughter discovers a hidden time - travel device in her father's old workshop. She decides to use it to go back in time to prevent her father's death. Along the way, she meets younger versions of the Avengers and has to convince them to help her without revealing too much about the future.
One idea could be a story where Tony discovers a hidden diary of Howard's that reveals secrets about his early inventions and the true motives behind some of his actions. This could lead to Tony having a new perspective on his father and his own work.
One idea could be that Tony Stark travels back in time to prevent the creation of certain dangerous technologies that later cause chaos in his timeline. He could use his genius to subtly alter the course of scientific development.
The de - aged Tony could also form a mentor - mentee relationship with a younger Avenger. He has the knowledge and experience of his older self but the energy and fresh perspective of his de - aged self. This relationship could be a key factor in how the story progresses, as he imparts his wisdom in a different way and the younger Avenger helps him see things from a new angle, which could potentially change the course of the Civil War in the fanfiction.
One plotline could be Peter struggling with choosing between Tony's side and his own moral compass. Maybe he tries to find a middle ground to keep his relationship with Tony intact while also doing what he believes is right.
One idea could be that Tony Stark is brainwashed by a powerful enemy. This enemy uses some advanced technology to manipulate his mind, turning him into a villain who starts attacking his former allies. He might use his Iron Man suits in new and devious ways against the Avengers.
A plot idea could be that a deaf hacker tries to break into Stark Industries' systems to prove a point about security flaws. Tony catches them but is intrigued by their skills. They start working together to improve security, with the deaf hacker using their unique observational skills. Another idea is that a deaf artist creates a piece inspired by Tony Stark, and he is so moved that he invites the artist to his tower. There, they face a threat together, and the artist's deafness becomes an unexpected advantage in outwitting the enemy.
One idea could be that Deadpool gets accidentally teleported into Stark Tower. He then proceeds to annoy Tony Stark with his non - stop chatter and crazy antics. Stark, at first, is irritated but then realizes Deadpool's skills could be useful in a new project he's working on.
Maybe the fanfiction could be about Tony adopting a child with special powers. He has to protect the child from those who would misuse the powers while also helping the child understand and control them. This could involve lots of action scenes and emotional bonding between Tony and the adopted child.