Jon Snow could be sent back to a time just before Ned Stark's father was killed. With his future - learned wisdom, he could try to save his grandfather and thus change the entire Stark family's fate. He may also discover secrets about his own lineage that were lost in time. This could lead to him having more power and influence in the past, as he might be able to claim certain rights or titles based on this new - found knowledge.
Another interesting plot would be if Jon Snow went back to the time when his father, Ned Stark, was a young man. He could interact with his father, perhaps change some small events that had big consequences later. He might also learn more about his family's secrets directly from Ned, things that were lost in time in the original story.
One plot idea could be Kagome accidentally traveling to the world of 'Game of Thrones' during a time when Jon Snow is in a great struggle. She could use her spiritual powers from her own world to help him sense approaching danger, like the White Walkers. For example, she might be able to detect their movements in a way that no one in Westeros can.
One idea could be that the demigods are sent back to prevent a great disaster that was actually caused by one of their own kind in the past. They have to figure out who it was and stop it without changing too much of the future.
One idea could be that Percy goes back to the time when the gods first came to power. He could try to change the way the gods interact with demigods from the start, leading to a whole new world order for demigods. Maybe he'd teach the early demigods some of the skills he has, like advanced sword fighting techniques.
One idea could be Jon Snow being the Kingsguard during a time of great political unrest in Westeros. He has to protect a young and inexperienced king from various assassination attempts by rival houses. Another plot could involve him having to choose between his loyalty to the king and his loyalty to his Stark family when a conflict arises between them. Maybe he discovers a dark secret within the Kingsguard that threatens the stability of the realm.
One plot idea could be that Jon and Sansa travel back to the time before their family's downfall. They could use their knowledge of future events to prevent Ned Stark's execution. For example, they might be able to expose Littlefinger's schemes earlier. Another idea is that they travel to a future time where the White Walkers have been defeated, but they find new threats emerging and have to figure out how to deal with them. They could also travel to different kingdoms in different eras and learn about different cultures and forms of governance, which could then help them better rule Winterfell and the North.
One interesting plot idea could be Percy going back in time to the era of the Greek heroes. He could meet Hercules and learn from him. Maybe he would have to face the same challenges Hercules did, but with his own modern - day skills and knowledge. Another idea is that he goes back to the time when the gods first emerged and gets involved in the power struggles among them. This could change the entire course of mythology as we know it.
A possible plot is that Anakin is sent back in time and ends up meeting his mother again when she was younger. This encounter could give him a chance to save her from the Tusken Raiders, which might then have a profound impact on his emotional state and his path in the Force. He could also use this opportunity to train himself differently, perhaps learning from the Jedi of that era in a more positive way, without the strictures that later led to his disillusionment.
One plot idea could be a story where Rhaella survives and somehow meets Jon Snow in secret. They could form an unlikely alliance against the threats to the Seven Kingdoms. Another could be a tale set in an alternate universe where Jon is born earlier and Rhaella plays a role in his upbringing, perhaps teaching him about his Targaryen heritage.
One plot idea could be Arya and Jon teaming up to uncover a long - hidden family secret. Maybe there's a lost Stark heirloom that has some sort of power, and they have to go on a quest to find it. Another idea is that they are both sent on a diplomatic mission to an unfriendly kingdom, and they have to use their unique skills - Arya's stealth and Jon's leadership - to succeed.