The plot might involve Naruto being influenced by some external force. For example, a new enemy could be using some kind of mind - control or illusion on him to make him ignore the Rookie 9. Another possibility is that Naruto has become so focused on his training to become stronger that he starts to neglect his relationships with the Rookie 9, thinking that his power is more important for the future of the village.
It could be Orochimaru. He's always been interested in Naruto and might come up with a plan to drive a wedge between Naruto and the Rookie 9. By making Naruto ignore them, he could be trying to isolate Naruto and make him more vulnerable to his attacks or manipulations.
One possible plot could be Naruto facing unexpected challenges during his rookie year that the original story didn't cover. For example, he might have to deal with a new group of enemies who are specifically targeting rookies. This would test his skills and his ability to adapt quickly.
Perhaps Naruto has a new power that he doesn't understand and it's making him act strange. This power could be related to some ancient jutsu. As a result, he starts to ignore everyone because he's afraid of hurting them or because he's constantly in a trance-like state due to the power's influence. His friends would then try to figure out what's wrong with him and how to bring him back to normal.
One possible plot could be that Naruto has been misinformed about Jiraiya's actions. Maybe he heard false rumors that Jiraiya was involved in something bad. So, he decides to ignore Jiraiya out of disappointment. As a result, Jiraiya has to find ways to prove his innocence and regain Naruto's trust.
Perhaps Naruto is being influenced by an outside force. It could be an enemy who has tricked him into believing that his team is holding him back. Or it could be that he has fallen into a dark state of mind, like if he has some kind of mental breakdown due to all the pressure he has faced in the past. In this state, he might just push Team 7 away without really meaning to in the long run.
A possible plot could be that the Rookie 9 are adults during a time when a new threat emerges that is related to an event from Naruto's past. They have to use their combined skills and knowledge from their years of growth to combat it. For example, if it's a resurgence of an old enemy from the Third Hokage's era, they need to figure out how to stop it before it destroys the village.
Maybe Naruto feels overshadowed by the Rookie 9 in the fanfiction. In the original series, Naruto has his own journey and development. If the fanfiction misrepresents his relationship with the Rookie 9 in a negative way, like making them seem better than him all the time, he could hate it.
Perhaps Percy has received some bad news or a prophecy that makes him think that by ignoring everyone, he can protect them. So he distances himself from his friends and family, and the fanfiction could explore how they react to his sudden cold - shoulder. They might try to figure out what's wrong with him and how to bring him back to his normal self.
A plot idea could be that Naruto, being older, is assigned to lead a special mission with the Rookie 9. He has to use his experience to keep them safe and complete the mission successfully. During the mission, he could teach them how to work together more effectively.
Maybe he got some kind of curse. In the Naruto universe, there are all sorts of dark magic and curses. If he was cursed, it could make him withdrawn and cause him to ignore everyone.