One idea could be Thor traveling back in time to prevent Ragnarok from happening in the first place. He could try to change the events that led to Hela's return, like stopping Odin from banishing Loki earlier. Another plot could involve Thor and his friends traveling to different time periods during Ragnarok to gather powerful artifacts to defeat their enemies. For example, they might go back to the time of the ancient Asgardians to find a weapon that can defeat Surtur.
Well, a cool plot might be that Thor travels through time during Ragnarok and ends up in an alternate version of Asgard. In this version, the events of Ragnarok have not occurred yet, but there are different threats. He has to work with the alternate versions of his friends and family to stop this new threat while also finding a way to get back to his own time and save his Asgard. It could involve some really interesting character interactions and battles.
One interesting plot idea could be the exploration of Asgardian characters' reactions to Thor's journey in Ragnarok from a different perspective. For example, how the common Asgardians felt about Thor's battles and his newfound friends. Maybe some of them were skeptical at first but then became inspired by his growth.
One character that could be added is the Enchantress. She could use her magic to either help or hinder Thor's time - travel attempts. Another could be Beta Ray Bill. He could team up with Thor in the different time periods they visit during their time - travel adventures. And perhaps the Warriors Three could be brought back through time - travel shenanigans, even if they died in the original Ragnarok storyline.
A cool plot could be that Thor and Tony have a bit of a rivalry at first. Thor thinks Tony is too full of himself with his high - tech gadgets, and Tony thinks Thor is just a brute with a hammer. But then they are forced to work together when an alien threat arrives that is immune to Tony's tech and Thor's brute force alone. As they get to know each other better, they learn to combine their strengths and defeat the enemy. They might even become good friends in the end.
One idea could be exploring Jane's further adventures on Earth while Thor is away in Asgard. Maybe she discovers some new scientific phenomena related to the Aether that was in her. Another could be Thor taking Jane to a secret part of Asgard that no human has ever seen before, and they face some challenges there together. Also, a plot where Jane gets kidnapped by an enemy of Thor's and Thor has to rescue her, but during the rescue he discovers some new powers within himself.
One idea could be Yoda traveling back in time to train Anakin Skywalker differently, thus preventing his fall to the dark side. Maybe he goes back to the very beginning of the Jedi Order to gain more knowledge about the Force and bring it back to his own time.
One idea could be Shinji traveling back in time to prevent the Second Impact. He might try to change the actions of his father that led to it. Another could be Asuka traveling to a future where the Evangelions have been completely forgotten and she has to figure out how to get back to her own time.
Another plot could be a character from the future coming back to the present in Shameless. They could be trying to stop a future disaster that is somehow linked to the Gallagher family. This would involve a lot of mystery and intrigue as they try to figure out what the future event is and how to prevent it while dealing with the chaos of the present - day Gallagher family.
One idea could be Goten traveling back to the Saiyan - Saiyan war era. He could end up changing some small events that have big impacts on the future, like uniting some Saiyan clans earlier. This would create a whole new timeline where relationships between characters are different.
Maybe a character travels forward in time and sees a dystopian version of the ACOTAR world. They then have to go back and try to prevent the events that led to that future. They could face many challenges along the way, like not being believed or having to work against powerful forces who benefit from the future they saw. It would be a race against time to save their world.
A possible plot for 'Haikyuu time travel fanfiction' is that Tsukishima travels back to his childhood when he first started to dislike volleyball. He could then understand why he developed that negative feeling and change his attitude from the start. This would lead to a much stronger Tsukishima in the present day. Another idea is that a team manager travels back in time to recruit a different set of players for the team, creating a completely different team dynamic. Maybe they could even bring back an old - school player who had unique skills that could revolutionize the team's playing style.