Well, a cool plot in an Arya Stark goes back in time fanfiction could be that she travels back to the time when the White Walkers first started to become a threat. Arya, with her knowledge of the future, could try to find a way to stop them from ever becoming such a powerful force. Maybe she'd team up with some of the early Night's Watch members in a way that changes the entire history of the war against the dead. Also, she could go back to the time when the Starks were still in a more powerful position in the Seven Kingdoms and use her skills to strengthen their alliances.
She might become more confident in her earlier years. In the original story, Arya faced many hardships that made her grow in a certain way. But if she goes back in time, having the knowledge of future events, she could be bolder in her actions and decisions from a young age. For example, she might be more assertive in dealing with Sansa when they were kids, and not let Sansa's girly ways get to her as much.
She might change the course of events in the past. For example, she could prevent some tragedies that happened to her family. Maybe she would use her advanced knowledge to help her father, Tony Stark, earlier in his life, which could potentially lead to a different future for the Avengers and the whole world.
One possibility is that Tony could prevent some of the major disasters that occurred in the Marvel Universe. For example, he might stop Loki from getting the Tesseract in the first Avengers movie. This would change the entire timeline and prevent the destruction of New York City that followed. Another thing is that he could meet his parents at a different time, which would be an extremely emotional encounter for him. He might also be able to use his advanced knowledge to help Howard Stark with some of his early inventions, potentially accelerating the technological progress of that era.
Sansa would be more assertive in her political moves. She has seen the consequences of inaction and bad decisions in the future. So, she would be quicker to make decisions that benefit her family and herself. For example, she might be more involved in military strategies to protect the North.
One idea could be that Sansa goes back in time and tries to prevent the Red Wedding. She could use her knowledge of the future to warn her family and change the course of that tragic event.
In a fanfiction about Arya Stark being pregnant, she might be in a situation where she has to keep her pregnancy a secret. Maybe she's in a land where her enemies are everywhere, and if they find out, they'll use it against her. She could rely on her skills of disguise and stealth to hide her condition as she tries to find a safe place for herself and her baby.
Well, she might try to prevent some of the tragedies that befell her family. For example, she could warn Ned Stark about the Lannisters' treachery, which could change the entire course of the story. Maybe she'd also use her assassin skills to take out threats before they even emerged.
Another theme could be Arya traveling to the future to see the long - term consequences of her actions in the original story. This can lead to some interesting self - discovery moments for her as she realizes how her choices shaped the world. Also, there are often themes of her using her time - traveling abilities to reunite with lost loved ones, like her family members who died in the original series.