At the start, Ash might underestimate Hunter J's yandere nature. He'd think he could just handle her like any other enemy. But as she starts to show her obsessive side, like targeting his Pikachu specifically or trying to isolate him from his friends, Ash would become more cautious. He would start to analyze her motives and actions more carefully. He might even try to find out if there's a way to cure her of her yandere tendencies, but if that's not possible, he'd be ready to battle her with all his might. His love for his Pokémon and his friends would fuel his determination to stand up to her.
One possible plot could be that Hunter J targets Ash for some unknown reason. Maybe she sees his unique bond with his Pokémon as a threat or something she wants to possess. Ash, being his usual brave self, has to outwit her while also protecting his Pokémon friends from her devious plans.
Naruto might be initially confused. He's used to people being friendly or at least straightforward with their intentions. So when Mikoto starts showing her yandere side, like getting overly possessive, Naruto would probably be like 'What's going on?'. He could try to talk to her and understand her behavior at first.
Naruto would probably be really confused at first. He's used to a loving mother figure, not a yandere one. He might try to talk to her and understand why she's acting so strangely.
Naruto might be really confused at first. He's used to people being friendly or having normal crushes, but a yandere is a whole different level. He'd probably try to talk to her and understand why she's acting so strangely.
He might be initially confused. Naruto is used to dealing with all kinds of opponents and situations, but a yandere Kyuubi would be a new and strange thing for him. He could try to reason with her at first.
Ash could get angry. He has a strong sense of justice, and he might feel that May has violated their friendship. He could challenge her, not in a violent way, but more in a way to get an explanation and to try to make her see the error of her ways. He would likely be determined to show her that what she did was wrong.
Ash would likely be shocked at first. He's so used to seeing the good in people, especially fellow trainers. But then he'd probably get angry and determined to set things right. He has a strong sense of justice, so he wouldn't let the betrayal go unpunished.
Naruto might also feel a sense of responsibility. He might think that he did something to cause Yugito to act this way. So he could start to limit his own actions to avoid triggering her yandere behavior. For instance, he might stop being so friendly with other girls in front of her. But at the same time, he would not give up his own dreams and values, and would try to make Yugito understand that her behavior is not acceptable in a way that is both firm and kind.
At first, Naruto might be really confused. He's used to the normal Sakura, so when she starts acting all yandere, he'd be like 'What's going on, Sakura - chan?'. He'd probably try to talk to her and find out what's wrong.
Obviously, Ash is one of the main characters. He is the Pokémon trainer on his journey to become a Pokémon Master. Hunter J is also a main character, a notorious Pokémon hunter who often causes trouble for Ash and his friends.