Pepper's character arc would be interesting too. She could become more involved in the superhero world. Maybe she starts to fund and support Peter's activities. She would also be dealing with her own grief, but at the same time, she might see it as her duty to ensure that Tony's sacrifice was not in vain. This could lead her to take on a more active role in protecting the world, similar to how Tony did, but in her own way.
Peter's character arc would take a very dark turn. He'd likely be consumed by grief and a sense of obligation. His once - carefree and enthusiastic approach to being a superhero would be replaced with a more solemn and determined one. He might become more secretive, not wanting to let others in on his pain.
One possible scenario in such a fanfiction could be that Peter, in a self - sacrificing move, takes on a powerful enemy that was originally meant to target Tony. Maybe Peter's inexperience and pure heart lead him to misjudge the danger, and he ends up giving his life to save others, while Tony is left to grapple with the guilt.
One possible plot development could be that Peter is left with a huge sense of guilt. He might struggle with survivor's guilt, constantly thinking that it should have been him. He could then become overly reckless in his superhero activities, trying to prove that he was worthy of being saved. Another aspect could be how the other Avengers deal with Tony's death. They may turn to Peter as a symbol of hope, since Tony sacrificed himself for Peter. This added pressure on Peter could lead to him either rising to the occasion or crumbling under it.
The story could focus on Tony's downward spiral into guilt and self - blame. He might isolate himself from the other Avengers, feeling that he should have been the one to die. His technological advancements could take a dark turn as he tries to find a way to bring Peter back, perhaps even dabbling in dangerous and unethical science.
If Hermione died instead of Sirius, it would be a huge blow to Harry and Ron. Hermione was the brains behind many of their plans. Without her, they might not be able to figure out how to fight Voldemort as effectively. For example, she was the one who discovered many of the secrets in the library. Also, her friendship was a source of emotional support for Harry, especially when he was dealing with his dark past and the challenges of being the Chosen One.
Well, Ginny would be devastated. Her relationship with Harry was budding into something more. With Harry gone, she might become more withdrawn. Sirius would feel a sense of guilt towards Ginny, as he's alive instead of Harry. He might try to be there for her like an older brother. The Weasley family as a whole would be in mourning. Their relationship with Sirius would be a mix of gratitude for still being there but also sadness that Harry was gone. And Snape's feelings would be complex. He might feel a strange sense of loss, as Harry was his connection to Lily in a way, and now he has to deal with Sirius still being alive.
Peter would likely become more confident. With Tony and Steve as his guardians, he has two great role models. He would learn different skills from them. From Tony, he might pick up more about advanced technology and using it in his superhero work. From Steve, he could gain more discipline and a stronger sense of justice. His character would also develop in terms of his relationships. He would become more family - oriented, learning the importance of having a support system.
Peter would probably be really confused at first. He looks up to Tony, and suddenly being kidnapped by him would be a huge shock. He might try to talk to Tony, asking him why he's doing this.
You can try looking on some popular fanfiction websites like Archive of Our Own (AO3). It has a vast collection of fanfictions, and there's a good chance you might find it there.
His character would develop a softer side. We know Tony as a tough NCIS agent. But with a daughter, he would show more tenderness. He might start to cry at her school plays or get overly excited about her achievements. His relationship with his female colleagues might also change, as he now has a different perspective on women due to being a father to a girl.
His patience would likely increase. Kids can be a handful, and Tony would need to learn to be patient. He might not snap as quickly at his colleagues when things get tough at work because he's getting practice in patience at home. He'd also become more empathetic. Understanding a child's needs would make him more in tune with the feelings of others in general.