In a 'Naruto Valley of the End Fanfic', Naruto and Sasuke are the primary characters that come to mind. But there are others who could be in the spotlight. Hinata, for example, as Naruto's wife in the later part of the series, could have a role. Maybe she accompanies Naruto to the Valley of the End for some reason. Shikamaru, with his intelligence, could also be involved. He might be the one to figure out some mystery about the Valley or help Naruto and Sasuke in a difficult situation there.
The main characters would surely be Naruto and Sasuke. Their final battle at the Valley of the End is a crucial part of the Naruto story. However, in a fanfic, characters like Itachi could also be brought in. His influence on Sasuke and his actions in the overall Naruto plot could be explored in relation to the Valley. And don't forget about Jiraiya. His teachings to Naruto could be revisited and related to Naruto's experiences in the Valley of the End.
Naruto is often a central character in naruto exams fanfic. His journey through the exams, with his determination and growth, is a common focus. His unique skills like the shadow clone jutsu play a big role in the exam scenarios.
Sasuke can also be a main focus. In a Tenketsu Naruto fanfic, Sasuke might have his own journey related to tenketsu. Maybe he discovers something about Naruto's tenketsu that makes him jealous or drives him to further his own power in a different way. Their rivalry could be intertwined with the concept of tenketsu.
Naruto is often still a main focus. Since he is the protagonist of the original series, fanfic writers like to explore different versions of him. But sometimes, other characters like Sasuke also get a lot of attention. Writers might make Sasuke more of a guiding figure for Naruto in a 'renegade' way, rather than just a rival.
Madara Uchiha might be the main antagonist. He has grand plans for the ninja world. He could see Naruto as a threat to his vision and engineer a situation in the Valley of the End where Naruto is killed, either directly or by using Sasuke as a pawn.
Obviously, Naruto himself would be a central character. Since the fanfiction is about his family being alive, Minato and Kushina would be major focuses too. They could play important roles in Naruto's growth, both as parents and as powerful ninja.
Obviously Naruto is the main focus most of the time. But other characters like Sasuke can also be important. Sasuke's own dark past and his relationship with Naruto can be further explored in a 'dark' context. For example, they might become rivals in a more extreme and less friendly way.
Sasuke is often a central character. Given his own struggle with hatred in the original Naruto series, fanfics might further explore his journey in the context of the curse of hatred, perhaps showing how he tries to overcome it in different ways.
The main character is Naruto without a doubt. But characters like Sasuke can also be important in these fanfics. Sasuke, as Naruto's rival, may be shown to have a different perspective on Naruto's past. Maybe he discovers something about Naruto's family or his own family's connection to Naruto's past that was previously unknown. And the Sannin, including Tsunade, could also be significant as they were part of the older generation with knowledge of events that could be related to Naruto's past.
Obviously, Neo would be a main focus as the name implies. Her mysterious and devious nature makes her a really interesting character to write about.
Oliver is an obvious choice. His journey from being a stray kitten to finding a new life could be further explored. For example, his relationships with the other animals could be delved deeper into, like his bond with Dodger.