I think Natasha would be the first to discover the truth. She's very perceptive and good at reading people. If she noticed something strange about Tony's behavior, she would start investigating. She has the skills to follow him secretly and figure out if he's really cheating or if there's something else going on. Maybe she'd find out that he's just trying to surprise Pepper with a big anniversary gift and all the secrecy is part of the plan.
One possible plot twist could be that Tony is actually working on a top - secret project that he has to keep from Pepper for her own safety. The Avengers misinterpret his secretive behavior as cheating. For example, he might be collaborating with a female scientist who has some unique skills relevant to the project. The Avengers see them together often and jump to conclusions.
Overcoming challenges together is also a big theme. Whether it's dealing with a new supervillain threat or internal issues within the Avengers, Tony and Pepper often face difficulties side by side. Fanfictions explore how their love helps them get through these tough times, and how they grow both as individuals and as a couple.
They might notice signs like Peter being overly withdrawn, flinching at sudden movements, or having unexplained injuries. Maybe they see him constantly on edge around certain people.
Maybe Tony has been lost in space or some other difficult situation. When he finally makes his way back, Pepper is waiting at the Avengers compound. Their reunion is filled with emotions. Pepper might be a bit angry at first for him putting himself in danger, but then she realizes how much she missed him and they share a passionate kiss.
Perhaps Pepper Potts would interact with each Avenger in unique ways. For example, she could have in - depth conversations with Tony Stark about how his superhero activities affect their business. With Captain America, she might discuss the values and ethics of the Avengers' actions. And with Thor, she could be fascinated by the Asgardian culture he represents.
If Pepper leaves Tony in the fanfiction, it could disrupt the Avengers' dynamic. Tony might become more withdrawn and less focused on the team, which could affect their mission planning. For example, he might not be as quick to come up with technological solutions during battles.
It could be some business rivals who see the daughter as a threat to their plans. They might try to undermine her or use her to get to Stark Industries.
Another storyline could be that they get involved in training the next generation of superheroes or tech - savvy individuals. They realize the importance of passing on their knowledge and skills. Tony could teach about advanced engineering and Pepper could offer her business and leadership expertise. This would be their way of ensuring a better future for the world.
There's a fanfiction called 'Pepper's Perspective'. This one gives a detailed view from Pepper's point of view. It delves into how she manages her relationship with Tony while being in the middle of all the superhero chaos. It's quite interesting as it shows her strength and her love for Tony in a new light. She has to deal with Tony's risky superhero stunts and also keep Stark Industries running smoothly.
Loki might be forced to tell the truth about his real intentions towards the Avengers all along. Maybe he reveals that he's actually a bit envious of their unity.