Naruto could also feel a sense of confusion. He might wonder what he did wrong or what made Fem Kyuubi choose Sasuke over him. This confusion could lead him to question his own worth and his relationships with others. However, in true Naruto fashion, he would eventually rise above these negative feelings and focus on his goals, like protecting the village and his friends.
At first, Naruto would likely be extremely shocked. He has always considered Sakura a friend and teammate, so this would be a huge blow. He might question his own judgment in trusting her.
Naruto would likely be initially shocked. He has always considered the Kyubii as a part of him and a friend in some ways. So the betrayal would be a huge blow to his sense of trust.
Ash might be initially shocked. He has always seen Sabrina as an acquaintance or even a friend in some cases. So when she betrays him, he'd be taken aback. For instance, he could freeze for a moment, unable to believe what has just happened.
Naruto might initially be in denial. He's so used to having Sakura around and believing that they have a future together. So when she leaves for Sasuke, he might think it's just a temporary thing or that she's been influenced by something or someone. But as time passes and he realizes it's real, he would be deeply hurt. He might also start to question his own self - worth, thinking that he wasn't good enough for Sakura. And he might even try to win her back at first, but then slowly come to accept the situation and focus on his other responsibilities like being a ninja and protecting the village.
At first, Naruto might be a bit scared or hesitant. But as the fem Kyuubi shows her caring side, like protecting him from danger, Naruto starts to trust her. As time goes on, they become more like family. The fem Kyuubi shares her wisdom with Naruto, and Naruto in turn shows her the value of human emotions.
He might be initially confused. Sasuke is not used to Sakura ignoring him as she has always been somewhat persistent in her attention towards him. So, he may be at a loss as to why she is suddenly acting this way.
Naruto might initially be shocked. Given his friendly nature towards Sasuke in the original story, he wouldn't expect such an attack from her. So, his first reaction could be pure disbelief.
In the long run, Percy might grow from the experience. He could become more cautious in his relationships and less trusting. Or, if there's a chance for redemption in the fanfic, he might be open to forgiving Annabeth if she shows true remorse and has a valid reason for her actions. But initially, it would be a very difficult and emotional time for him.
Issei would probably first try to understand why Rias has betrayed him. If he finds out that she was forced or manipulated, he might try to save her. But if it was a conscious choice, he could become angry and vow revenge. He has a strong will, and this betrayal could fuel his determination to become stronger on his own.
Neji might get angry. He's a proud character, and being called a girl in a somewhat derogatory way (if that's how he takes it) could make him lash out at Naruto. He could give Naruto a cold stare and tell him to watch his words.