Well, his time - travel might create alternate timelines. If he changes a significant event, like preventing a major villain from rising to power in the past, the whole future could be rewritten. There could be new friendships, new enemies, and new power dynamics. The shinobi world as he knew it might cease to exist, or at least be very different.
If Kakashi travels back in time, his actions could have a butterfly effect. For example, if he saves someone who was supposed to die, that person's actions in the future could be completely different. This could lead to changes in alliances, battles, and even the political structure of the village.
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.
The marauders' presence in 1995 would likely disrupt the normal flow of things. They could influence the relationships between the characters. For example, they might become friends with the Weasley family and introduce some new pranks or ideas to them. Their knowledge of the past could also help in dealing with Voldemort, but it could also create confusion as they may not fully understand the current situation. And they may have some conflicts with certain characters who don't trust their sudden appearance.
One common theme is redemption. Since Kakashi can go back in time, he often tries to make up for past mistakes or prevent tragedies that occurred in the original timeline. For example, he might try to save a character who died before. Another theme is the changing of fates. He can change the destiny of not only himself but also of his friends and the whole village. He can use his knowledge of future events to better prepare for threats.
If Gohan travels back in time, his relationship with his father, Goku, would be really interesting. He could train with Goku as an equal, which would be a different dynamic from their usual father - son - student - teacher relationship. Goku would probably be surprised but also excited to have such a strong partner to train with.
For Boruto, time traveling might make him more appreciative of the past and how hard his father worked to build the world he lives in. He could become more humble and learn from the simplicity and determination of the past generations. His friends, too, might gain a new perspective on their own lives. For example, Sarada could see how her mother was as a young kunoichi and understand her better.
For Naruto, if Rikudou Sennin travels back in time, he could potentially train Naruto earlier. This would make Naruto much more powerful at a younger age and might change the way he faces his enemies like Sasuke. Naruto could also learn some ancient jutsu directly from the Rikudou Sennin.
In a time - travel scenario, their relationship could develop in many ways. At first, they might be strictly in a teacher - student type of relationship as they always were. But as they face the challenges of the past together, they could become more like equals. For example, Sakura might come up with a plan to deal with an old - time enemy using her modern - day knowledge, and Kakashi would have to respect her for that. They might also develop a deeper bond of trust as they rely on each other to survive in a strange time. And perhaps, there could be some moments of self - discovery for both of them as they see how they fit into the past and how they've changed from who they used to be.
If Naruto travels back to the past, his relationship with his parents would be completely different. He would finally get to meet them as an adult and be able to have proper conversations with them. He could share his experiences and they could give him advice from their own wisdom.
If Dumbledore traveled to the past and influenced important historical figures, it could change the political and social structure of the wizarding world. Say he convinced a key figure to support a different ideology. This could lead to different laws and norms in the present. It might also change the relationships between different magical communities, like how wizards interact with goblins or centaurs.
It would greatly affect Jon. If their son travels back to the time when Jon was still at the Wall, he could reveal to Jon his true identity earlier and help him accept his Targaryen heritage more smoothly. This could change Jon's actions and decisions. For Daenerys, the son could give her more confidence in her claim to the Iron Throne by showing her the future support she could have had.