Naruto himself is very likely to be central. Since he is the main character in the original series, any alteration of time would likely still revolve around him in some way. His journey and how it's affected by the time changes would be a major focus. Sasuke is also a prime candidate. His relationship with Naruto and his own quest for power and revenge could be greatly altered by time changes. Another one could be Kakashi. He has a lot of backstory and knowledge, and in an altered time, his role as a mentor or a ninja in general could be very different.
Definitely Naruto and Sasuke, as their fates are intertwined in the original story. In a time - altered scenario, their bond and their individual destinies would be ripe for exploration. Hinata could also be central. In the original, she had a strong, if somewhat understated, presence. In a time - altered fanfiction, her relationship with Naruto might be completely different, and she could play a more prominent role in the events of the ninja world. And then there's Itachi. His actions were so crucial in the original story that any time alteration could have a huge impact on his story and how it affects the other characters.
Well, Naruto is the obvious choice as he is the protagonist. But I think Jiraiya could also be central in time alter fanfiction. He has a vast knowledge of the ninja world and was a key figure in Naruto's development. In an altered time, his teachings and his own adventures could be very different. Also, Nagato. His role in the original story was significant, and in a time - altered world, his views on peace and his actions could be completely changed. He might not form the Akatsuki in the same way or might have different goals altogether, which would have a huge impact on the overall story.
Naruto is still often a very popular character in such fanfictions. Since it's about altered powers, his character provides a great base to explore different power - up scenarios.
I think Weiss could also be central. She comes from a powerful family and has a lot of influence. In a story about watching the future, her knowledge of politics and her strategic thinking could play a big role. Also, her relationship with the other characters, especially Ruby, would be important in how they all react to what they see in the future. Blake might also be central as she has her own complex backstory and her views on the relationship between humans and Faunus could be greatly affected by seeing the future.
Sasuke would be a likely character to interact with Naruto as a Time Lord. Their complex relationship in the original Naruto series would add an extra layer of drama in a time - traveling scenario. Another could be Kakashi. His wisdom and experience would make for interesting conversations with Naruto, especially when Naruto has the power of a Time Lord. And of course, Jiraiya. Given his close relationship with Naruto and his own adventurous spirit, he'd be very involved in Naruto's time - traveling adventures.
Sasuke could also be a character who breaks the time loop. He is highly intelligent and has a thirst for power and knowledge. If he realizes that he is in a time loop, he would likely be very intrigued and start investigating. His Sharingan might give him some insights into the nature of the loop and help him find a way to break it.
Naruto, Sasuke, and Sakura are the most obvious choices. They are the main characters and their interactions are always interesting. Naruto would bring his energetic and fun - loving nature, Sasuke his brooding intensity, and Sakura her intelligence and strong - willed personality.
Naruto himself could be in jail fanfiction. Maybe he was framed for a crime he didn't commit and has to prove his innocence from within the prison. Sasuke is also a likely candidate. His brooding and sometimes anti - social nature could lead to him getting into trouble with the law in a fanfiction setting. Another one could be Orochimaru. Given his history of unethical experiments, it's not hard to imagine him ending up in jail in a fan - created scenario.
Naruto is a very likely character. Given his strong will and connection to the Nine - Tails, he would be motivated to time - travel to fix problems related to the Juubi. His ability to make friends and influence people would also play a big role in any time - traveling story.
Definitely Kakashi. He's already very intelligent and has a wide range of skills. Time control could be an addition to his arsenal, and he could use it in creative ways in battle or for teaching purposes. Also, Madara Uchiha could be a likely character. He was always seeking more power, and time control would be a very powerful ability for him to have in fanfiction.
Akeno could be a central character as well. Her unique powers in 'Highschool DxD' could be further developed with the addition of 'Fate' and 'gamer' elements. For instance, she could gain new skills or abilities through the 'gamer' system and use them in 'Fate' - like battles, making her a key figure in the fanfiction.
Iron Man is another candidate. Tony Stark's technology and Naruto's ninja techniques could be a great contrast. They could learn from each other. Stark might be interested in Naruto's chakra - based powers and try to replicate them in some way, while Naruto could be amazed by Stark's high - tech gadgets.