One interesting idea could be Tsuna going back in time to prevent certain tragedies in his family's past. This would change the whole dynamic of the Vongola family in the present.
Another plot could be Tsuna traveling back to a time when his father was still around. He could get to know his father better and learn some hidden family secrets. This would not only strengthen their relationship but also give Tsuna an edge in his future as the Vongola boss. He might learn about some special powers or techniques that his father knew but never got to pass on to him in the original timeline.
One idea could be Tsuna, as a girl, discovers she has unique powers that are only passed down to female members of her family. She then has to navigate the challenges of keeping it a secret while also using her powers to protect her friends and family. Another could be that she is a girl in an all - boy school and has to deal with the various reactions from her male classmates, from admiration to jealousy.
One interesting plot could be Naruto using his ninja skills in the world of Tsuna. For example, he might use his shadow clone jutsu to help Tsuna deal with multiple threats at once. Another could be Naruto teaching Tsuna some of his unique chakra control techniques which could enhance Tsuna's own combat abilities in his world.
Well, a plot could revolve around them building their dream home. Haru might have very specific ideas about how the home should look and feel, while Tsuna is more concerned about the security aspects. They have to compromise and work together to create a home that is perfect for both of them. This could also involve some comical moments when contractors don't understand their requests or there are unexpected problems during construction.
One idea could be a story where Tracer accidentally travels back to the Omnic Crisis era. She could meet the younger versions of the original Overwatch founders and try to help them in ways that might change the future of Overwatch. Another could be Reinhardt going back in time to his early days as a Crusader and having to relive some of his toughest battles with the knowledge he has now.
One interesting idea could be Itachi traveling back in time to prevent the Uchiha massacre. He could use his knowledge of future events to find a way to resolve the conflict between the Uchiha clan and the village without bloodshed. Another idea might be Itachi traveling forward in time to see the consequences of his actions and how his younger brother Sasuke has turned out. He could then try to guide Sasuke in a different direction from the future he witnessed.
One interesting idea could be the characters going back in time to prevent certain tragedies. For example, they might try to stop the deaths of some important characters. This could change the whole course of the story and create new relationships and plot twists.
One idea could be Atsushi traveling back to his own past to prevent certain tragedies from happening in his life. He might change the way he was treated in the orphanage or avoid some of the early hardships. Another idea is Atsushi traveling to a future where he has become a much more powerful and respected figure, and he has to learn from that future self to come back and save his present world. And a third idea could be Atsushi getting accidentally sent to a different time period in Yokohama's history and having to navigate through that era while also trying to find a way back to his own time.
In a Ninjago time travel fanfiction, the ninjas could be sent forward in time to a post - apocalyptic version of Ninjago. They would have to figure out what went wrong and then travel back to their own time to prevent it from happening. This could involve battles with future versions of their enemies who have evolved into even more dangerous foes.
One interesting idea could be changing the outcome of key battles. For example, if a character travels back in time, they might be able to prevent a certain loss in a fight, which could then change the entire course of the story. Another idea could be related to relationships. A character might go back in time to fix a broken relationship or to start a relationship earlier than it originally happened in the ff8 universe.