Well, in a Naruto and Yoshina time travel fanfic, a lot could happen. They might go back to key moments in Naruto's history. For example, they could end up during the Nine - Tails attack on Konoha. Yoshina might use her unique abilities, whatever they are in this fanfic, to help Naruto deal with the situation differently. Maybe they could prevent some of the tragedies that occurred in the original story, like the death of some important characters. This would then change the whole course of the Naruto universe as we know it.
In this fanfic, if they time travel, they could also meet alternate versions of themselves or other characters. Naruto might meet a version of himself that made different choices in life and learn from that experience. Yoshina could interact with different versions of Naruto's friends and enemies, which would be really interesting. This could lead to all sorts of character development and new storylines, like forming unexpected alliances or uncovering secrets about the Naruto universe that were previously unknown.
One interesting plot could be that Naruto and Yoshina time travel to the era of the Sage of Six Paths. They could learn about the origin of chakra directly from the source. Naruto might gain new powers or a deeper understanding of his own abilities. Yoshina could also have her own revelations. Another plot could be that they are sent back to when Naruto was a child and they have to prevent Orochimaru from infiltrating the village earlier. This would change the power dynamics in the village and Naruto's growth path.
Well, in a Commander Rex time travel fanfic, he could go back to crucial battles and change the outcome. Maybe he'd prevent some of his comrades from dying. For example, he could go back to the Clone Wars and use his future knowledge to outwit the Separatists more effectively. He might also meet his younger self and give some valuable advice, like how to better handle difficult situations or make wiser decisions in the heat of battle.
In such a fanfic, Naruto might be shocked by the advanced technology in the future. He could see flying cars and buildings that reach the sky. His ninja skills would be put to the test in a whole new environment where physical strength might not be as dominant as it was in his time.
Well, one possibility is that Naruto with the Rinnegan could use his newfound power to protect Kushina during their time travel. Maybe he can prevent some of the tragedies that happened in the past. For example, he could stop the Nine - Tails attack on the village by controlling the beast in a more efficient way with his Rinnegan powers.
Well, one possibility is that Naruto could learn a great deal more about the past of the ninja world directly from Jiraiya. He might also get to witness some of the key events that shaped the present he came from. For example, he could be there when Jiraiya was gathering information on the Akatsuki, which would give him a huge advantage in dealing with them in his own time.
Well, Naruto could go back in time and train his younger self. He'd be able to pass on all the skills and knowledge he has as the 6th Hokage. This would make his younger self much stronger and more confident much earlier in life.
Well, they could end up in different historical events. Maybe they land during the Saiyan - Tuffle war. Kid Goku might be confused but Android 18 could use her knowledge of history (if she has any in this fanfic) to guide them. They could also meet different versions of characters, like a younger Vegeta or Gohan.
In this kind of fanfic, a lot could happen. Maybe Anakin could use time travel to prevent his fall to the dark side. He might go back and make different choices, which would then change the entire future for Luke and Leia. Padme could also be involved in this time - traveling adventure. For example, she could use her knowledge of future events to try and save the Republic in a more effective way. And Luke and Leia, they might end up traveling through time as well to learn more about their parents' past and the history of the Jedi and Sith.
She could go back in time to meet Tom Riddle when he was still a student at Hogwarts. This would be an interesting encounter as she could try to influence him in different ways compared to what actually happened in the original story.
Well, Harry might find himself in a time when James' brother was at Hogwarts. He could witness their school days and how the family dynamics were different back then. Harry could form an unexpected friendship with James' brother, which would give him new insights into his father James and the entire Potter heritage.