His sense of justice could be warped. He may start to use more violent and unethical methods to achieve his goals. Maybe he doesn't care about collateral damage anymore and just focuses on getting revenge or power.
He might become more cynical. Instead of seeing the good in people like he used to, he starts to suspect everyone's motives. For example, he may no longer trust his friends easily.
His once optimistic and determined personality would turn cynical. Instead of seeing the good in people, he would suspect everyone. For example, he would no longer trust his friends easily. His sense of humor would disappear, replaced by a cold and sarcastic attitude. He would become more secretive and withdrawn, not sharing his thoughts and feelings like he used to.
His personality might become more aggressive. The demon nature could bring out his primal instincts, making him less patient and more prone to anger.
Naruto might become more calculating. Since Mewtwo is very intelligent and has powerful psychic abilities, Naruto would have to use his mind more. He would think before acting, unlike his impulsive self in the original series. This change could make him a better strategist in battles, but it could also lead to misunderstandings with his friends who are used to his more straightforward and impulsive nature.
Naruto's personality could shift towards being more reserved. As a Shinigami, he has to deal with the weight of handling souls and the concept of death. This could make him think twice before acting impulsively like he used to. He may also develop a more empathetic side towards those who are about to die or have lost loved ones, as he now has a closer connection to the afterlife.
If Naruto becomes a Hunter Nin in fanfiction, his personality would change significantly. He'd be more calculating. His usual impulsive nature would have to be toned down because one wrong move as a Hunter Nin could mean disaster. He might also become more solitary, used to working alone in the shadows rather than in a team. His sense of humor might also be more subdued as he takes on this serious and dangerous role.
He might become more serious. He realizes the weight of his responsibilities, so he's not as carefree as before. But he still tries to keep his positive and determined attitude.
His positive and determined personality would turn into a cynical and cruel one. He might lose his sense of justice and become self - centered.
His personality would become more reserved. As an assassin, he couldn't be as open and friendly as he used to be. He'd have to keep his emotions in check to avoid being detected.
Naruto's personality would become more brooding. He would be less impulsive and more calculating, like Batman. He might not be as openly friendly as he was before, keeping his thoughts and plans more to himself.
His character might become more isolated. With the power of the Juubi, Naruto may feel that he's on a different level from his friends. He could also become more cautious as he has to control such a huge power.