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.
Kakashi could be influenced as well. Rikudou Sennin could pass on some knowledge about Obito's situation earlier. This would allow Kakashi to better handle Obito's fall and might prevent some of the tragedies that occurred later. It would also change the way Kakashi trains Naruto and Sasuke.
Maybe he travels back to the time when the ninja clans were first forming. He could influence the way the ninja system is developed, for example, by promoting more peaceful co - existence among clans from the start. This would lead to a very different Naruto world where the concept of hidden villages might not even exist in the same way.
His powers could be integrated in a really cool way. For example, the Rikudou Sennin's ability to control all the chakra natures might translate into some sort of unique magic control in the DxD universe. Maybe he could use his Sage Mode to enhance his perception of the supernatural elements in DxD. Since he has the power of the Ten - Tails, it could be something like a super - powerful familiar or a source of immense energy that he could draw from in battles against devils, angels, and fallen angels.
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.
Some characters might be in awe. For example, Naruto himself would probably be excited to meet the reborn Rikudou Sennin, hoping to learn more about the origin of chakra and how to further peace in the ninja world. However, characters like Sasuke might be more cautious. He would be wary of the power the reborn Sennin holds and might suspect his intentions, especially if the reborn Sennin shows any signs of disrupting the current balance of power.
Naruto himself is often a popular choice. Fans like to see him go back in time and use his future knowledge and skills to change things. Sasuke is also quite popular. His complex backstory and powerful abilities make for interesting time - travel scenarios. Another popular character is Kakashi. He has a lot of mystery and potential for development in time - travel stories, especially with his Sharingan and his relationship with Obito.
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.
If Minato time - travels, it could change a lot. For instance, if he prevents the Nine - Tails attack, Naruto would grow up in a very different environment. He might not be the underdog he was in the original story. Also, if Minato changes things during the Uchiha clan's situation, Sasuke's story would be completely different. Konoha's political situation would also be altered. There would be less animosity between different clans perhaps.
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.
Fem Naruto's personality might bring a new perspective to the time travel story. She could be more diplomatic, using her charm and femininity to negotiate in situations. This would contrast with male Naruto's more head - on approach. Shikamaru, with his observant nature, would notice small details in the past that could be crucial. However, his tendency to overthink could cause delays in their actions. Their combined personalities would create a unique dynamic. Fem Naruto might push Shikamaru to be more proactive, while he might keep her from making rash emotional decisions.
Yes, in some fanfictions, Naruto can be depicted as the Rikudou Sennin. Fanfiction writers often take creative liberties and come up with unique storylines where Naruto might inherit the powers or even be reincarnated as the Rikudou Sennin to explore different plot developments and character arcs.