Well, the storyline could change in many ways. For example, if Naruto goes back in time, he might prevent some of the tragedies that happened in the original story. He could stop the Uchiha massacre, which would completely change Sasuke's story arc. Also, he might be able to train with the earlier versions of his teachers and learn new jutsu much earlier, making him even more powerful in the future timeline.
In the past, Naruto could gain the ability to change the fates of characters. This isn't exactly a traditional ability, but it's very important. By changing the past, he could make his friends stronger in different ways. For example, he could ensure that Rock Lee gets proper medical treatment earlier, which might allow Lee to develop even more powerful taijutsu techniques. This, in turn, would change the dynamics of battles and how Konoha as a whole approaches combat.
One possibility is that Harry would use this opportunity to change certain events in the past that had a negative impact on the baby or its family. He could also form a special bond with the baby. Maybe he'd introduce the baby to some of his friends from his own time who are also in the past now. This could create a whole new set of relationships and storylines in the fanfiction.
One possible scenario could be that all of Naruto's friends are killed in a great battle. He survives but is left alone, haunted by the memories of his lost comrades. He might then wander the world, a solitary figure, with his only company being the memories of the past.
Well, he might join a magic guild. Since Naruto is strong and has his own set of skills like ninjutsu, he could easily adapt to the magic battles in Fiore. Maybe he'd learn some magic too, combining it with his ninja abilities to become an even more formidable fighter.
He might use his ninja skills to survive in Westeros. His ability to move stealthily and his combat skills could make him a formidable figure. He could also form alliances with some of the characters in Westeros, perhaps teaching them some of his ninja techniques in return for knowledge about the land.
Well, he might be completely out of his depth at first. Naruto's ninja skills are cool, but in the DBZ universe with all those super - powered Saiyans and other strong beings. He'd probably try to make friends and learn about the new world. Maybe he'd try to use his Rasengan against a Ki blast, which would be an interesting sight.
In this kind of fanfiction scenario, Naruto could face challenges from future villains who have powers he's not familiar with. However, his own experience and strong will would still be valuable assets. He might also meet descendants of his friends and discover how his actions in the past have influenced the future in ways he never expected. For example, he could find that a village was founded in his honor, or that a new style of ninja training was developed based on his teachings.
Well, he might try to expose Voldemort earlier in his rise to power. Harry could use his knowledge of Voldemort's Horcruxes to start looking for them right away. Also, in the past, he could form new alliances. Maybe he teams up with some of the older generations of wizards and witches who were previously unaware of Voldemort's true intentions. And his presence in the past could cause a stir in the wizarding world as people try to figure out who this mysterious boy is with such strange knowledge.
Definitely his professors when they were younger. For example, Snape as a student. This would be a strange interaction considering their relationship in Harry's own time. He could also meet Hagrid when he was just starting out at Hogwarts. And there's a good chance he'd run into Sirius and Remus during their school days, and perhaps form new friendships or alliances with them in the past.