Imagine Boruto going back to the time of the Nine - Tailed Fox attack on Konoha. His relationship with Minato, Naruto's father, would be complex. He would have to be careful not to disrupt the events that are meant to happen in the future. He might befriend Minato and help him in some small ways during the chaos of the attack. This would create a unique bond between them that is different from the normal family connection. And his relationship with the other villagers during that time would be based on his ability to prove that he is there to help and not cause more trouble, which would be a big challenge for him.
When Boruto goes back in time, say to the era of the Third Hokage. His relationship with the village elders and the teachers at the ninja academy would be completely new. He would be seen as an oddity since he has knowledge and skills that are not from that time. He might form unexpected friendships with some of the young ninjas of that era. His relationship with his own family members in the past, like his grandparents, would also be very interesting. He could learn a lot about his family's history and values from them, which would change how he views his family in his own time.
If Sasuke travels to the past, his relationships would be completely transformed. With his clan members, he would have a chance to interact with them in a new light. He might try to warn them about their impending doom, which could change the dynamic from one of normal family relations to one of him being a seer of sorts. Regarding Kakashi, Sasuke could either use his knowledge of Kakashi's teaching methods to his advantage or try to change how Kakashi trained him. And when it comes to his enemies in the past, like Orochimaru, Sasuke might approach him differently. He could try to avoid Orochimaru's influence altogether or try to turn Orochimaru into an ally against the greater threats that he now knows about from the future.
Their relationships would likely become stronger. They would have to rely on each other more in the unfamiliar past environment. For example, Naruto might look up to Kakashi even more as he sees how much Kakashi has grown and changed. Sasuke might be more open to the idea of teamwork as they face challenges together in the past.
Boruto and his friends would face many challenges in adapting to the past. They are used to modern conveniences like instant communication devices. In the past, they'd have to rely on messengers or their own physical abilities to communicate. Also, they'd need to adjust to the different fighting styles and weapons. The ninjutsu they know might be too advanced for the past, so they'd have to be careful not to show off too much and draw unwanted attention. They might also struggle with the food and living conditions which were much more primitive compared to their time.
If Merlin travels back in time, his relationship with Arthur would be very different. In the past, Arthur might not trust him at all at first. Merlin would have to prove himself all over again. With Gwen, he might be more aware of her future importance and try to protect her in a different way. And his relationship with the other knights could be completely new, as they might see him as a stranger with strange powers.
If Natsu goes back in time, his relationships would be very different. With his friends, he might have a new level of understanding. For example, he could see how they grew up and the challenges they faced in the past. He might be more protective of them, especially if he knows what's going to happen in the future. His relationship with Lucy could also change. He could see her in a new light, perhaps realizing things about her that he didn't before when he first met her in the present.
His relationship with Sasuke would be different. Without the shared experience of being outcasts in the village, they might not have the same initial bond. Naruto would have a stronger support system from his Uzumaki family, so he might not be as desperate for Sasuke's friendship in the same way.
One possible storyline could be Boruto going back in time to the era of the Fourth Great Ninja War. He could use his knowledge of modern jutsu to change the outcome of certain battles. For example, he might help prevent some of the casualties that occurred. Another idea is that he travels back to the time when his father, Naruto, was a child. Boruto could then learn more about Naruto's early struggles and perhaps gain a new perspective on his own life and the legacy he has to uphold.
In a time - travel scenario, Anakin's relationship with his mother could be greatly altered. He could go back in time and save her from the Tusken Raiders. This would change his whole outlook on life and his path towards the dark side. Regarding his relationship with Palpatine, he would be aware of Palpatine's true nature from the start. So, he could either avoid Palpatine completely or try to expose him earlier. His relationship with other Jedi, like Ahsoka, could also be different. He could be a better teacher and mentor to her, as he has the experience of his future mistakes.
If Kakashi travels back in time, his relationship with his father would be completely different. Instead of the strained relationship due to his father's perceived failure, he could support his father and build a strong bond. With his students, if he travels to the future and then back, he might have a new perspective on how to train them. He could be more lenient or more strict depending on what he saw in the future of their development.
If Bilbo goes back in time to when he first met the dwarves, his relationship with them would be quite different. He would already know them well, and they might be more suspicious of his prior knowledge. But he could also use this to his advantage and form even stronger bonds with them more quickly, as he would understand their personalities better from the start.