He might initially be in shock and disbelief. Naruto has always valued his friends highly, so it would be a huge blow to him. He could try to reason with them at first, asking them why they are doing this.
Naruto could also feel a great sense of sadness and loneliness. He might isolate himself for a while, reflecting on what went wrong. However, his strong spirit won't let him be defeated for long. He'll gradually start to build new relationships or focus on his existing relationships with those who still believe in him, like Iruka - sensei. And he'll use this experience as a motivation to become a better ninja and a more understanding person, so that he can prevent such a situation from happening again in the future.
He would probably try to figure out what went wrong. Harry is a curious and determined character. He might start to recall recent events to see if there were any signs of his friends' discontent. He could also try to reach out to them, either directly or through mutual acquaintances, to ask for an explanation.
At first, Naruto would be in disbelief. He has always trusted his friends wholeheartedly, so this would be a huge blow. He might then feel a deep sense of anger and sadness. However, Naruto being Naruto, he would likely also start to look for ways to prove his innocence or the misunderstanding. He might go on a journey of self - discovery to figure out what went wrong and how he can win back his friends' trust, all while dealing with the pain of the betrayal.
Sometimes, Naruto will try to understand his friends' motives. He's a very empathetic person deep down. So instead of just getting angry and staying that way, he'll try to figure out why his friends did what they did. He might even forgive them relatively quickly if he realizes they had good intentions, even if their actions still hurt him.
In some fanfictions, Naruto may become extremely bitter. He could feel a deep sense of betrayal and this might fuel his determination to become stronger, not for the sake of the village at first, but more for self - vindication. He might isolate himself from others and struggle with his identity.
Naruto would be extremely hurt. He values his friends above almost everything, so their betrayal would be like a knife to the heart. At first, he'd probably be in disbelief and try to reason with them. When he realizes they won't listen, he might become angry and lash out. But deep down, he'd still hope to win them back.
Naruto could also get really sad and start to doubt himself. He might think that he did something terribly wrong, even if he didn't. And he may try to change himself to win back their friendship, like suppressing his usual exuberant personality.
He would be heartbroken. Naruto values friendship above almost everything. At first, he might not believe it and try to reason with his friends.
His friends would likely be in shock. Sasuke, for example, might initially be angry at himself for not being able to prevent this. He would then start planning ways to break the seal and get Naruto back. Sakura would be heartbroken. She might use her medical skills and knowledge of chakra to try to find a way to communicate with Naruto or at least sense his condition in the moon. Shikamaru, being the strategist, would start gathering information about the seal and who or what caused it.
In some fanfictions, Naruto might become more withdrawn at first. He could focus on self - improvement, training harder to prove himself. He might also start to question his self - worth since his friends' abandonment makes him feel unwanted.
Ash could respond in different ways. He might try to confront his friends immediately to get an explanation. If the betrayal is really bad, he could cut them off completely and focus on his own goals, like becoming a better Pokémon trainer. He would also probably have some internal struggles, as he has memories and experiences with these friends that he can't just forget.