Well, he could start a sort of technological revolution in Thedas. Since Tony Stark is known for his Iron Man suits, he might try to recreate a version of it using the resources available in Thedas. This could lead to a whole new way of warfare or defense in that world. He may also have to deal with the political and social implications of introducing such advanced technology. Some might see it as a threat to the existing power structures, while others might see it as a way to gain an edge in the constant conflicts that exist in Thedas.
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 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.
A great plot could involve deaged Tony getting involved in the early days of Stark Industries. He might see things from a new perspective and try to change the company's direction towards more ethical practices right from the start. This could lead to all kinds of adventures as he tries to convince the adults around him to listen to him. He could also form unexpected friendships with employees who later become important in the 'grown - up' Tony's life.
One idea could be that Tony leaves Earth to find a new energy source for the planet. He travels to a distant galaxy where he encounters strange alien races and has to use his intelligence to bargain for the energy. Another could be that he leaves because he feels ostracized after the events in Endgame and he goes on a journey of self - discovery among the stars.
One idea could be that the kidnappers are from a rival tech company trying to steal Stark's latest inventions. They hold him hostage in an abandoned factory and he has to use his wits and some makeshift gadgets to escape. Another plot could involve a group of villains who want revenge on Stark for past defeats and they kidnap him to lure his superhero friends into a trap. A third idea is that a mysterious organization kidnaps him to force him to build a powerful weapon for their own evil purposes.
One plot idea could be that they discover their 'brotherhood' through some magical or scientific accident. Maybe they have to team up to stop a common enemy, like an ancient, powerful being. They could start off hating each other because of their different personalities (Tony's brashness vs Loki's slyness), but as they face challenges together, they learn to respect and care for each other.
One idea could be a story where Tony and Natasha have to go undercover as a couple on a mission. They start to develop real feelings during the process. For example, they might have to attend a high - society event and deal with all the pretenses while also trying to uncover a hidden enemy. Another plot could be set in a post - apocalyptic world where they are two of the few survivors and have to rely on each other completely to stay alive and rebuild society. Or perhaps a story where they both get trapped in a virtual reality world created by an enemy and have to find a way out together while also facing their own inner demons.