In such a fanfiction, Harry's personality would be a far cry from the kind - hearted boy we know. He would be more aggressive, as he'd be taught to fight and assert dominance in a more brutal way. He might lack empathy since the villains would not likely foster a sense of compassion in him. Also, he could be more secretive and scheming, always looking out for his own interests first and foremost, rather than thinking about the greater good of the wizarding community like in the original Harry Potter series.
His personality would likely be more cold and calculating. He'd be used to getting his way through underhanded means taught by the villains.
Harry's personality would be a lot more complex. Instead of the somewhat naive and overly - trusting Harry we know, he would be more calculating. Loki's influence would make him question people's motives more. He would also be more confident in his abilities, not just relying on his friends all the time. He might have a darker sense of humor too, given Loki's nature. And his sense of loyalty could be more conditional, depending on what he could gain from a relationship.
He'd be more reserved. Vergil isn't exactly a talkative and outgoing person. Harry would likely follow suit, keeping his thoughts and feelings to himself more often.
He might become more reserved. Shinobi are often taught to keep their emotions in check, so Harry would be less likely to be as openly angry as he sometimes is in the original story.
His personality would be more aggressive. Yautja are hunters, and growing up with them, Harry would adopt their aggressive nature. He would be more direct in his actions and less likely to hesitate.
If Harry Potter was raised by Natsu, his personality would change drastically. Natsu is a very passionate and hot - tempered character. Harry would be influenced by this passion and would be more driven in his pursuits. He would no longer be the meek boy who was bullied by the Dursleys at the start. Instead, he would be more confident and assertive. His sense of justice would also be more like Natsu's, which is more about immediate action rather than following a set of bureaucratic procedures. He would probably have a stronger sense of loyalty towards his friends as well, because Natsu values friendship above all else and would instill this value in Harry.
His personality might become more reserved. Growing up with a Shinigami would expose him to different values than the normal wizarding ones. He might not be as quick to trust or be as carefree as in the original story. Instead, he'd be more cautious and perhaps a bit more brooding, always thinking about the deeper meaning of things and the consequences of actions.
His personality would be greatly influenced by the forest environment. He would be more wild and free - spirited. Growing up away from the constraints of wizarding society, he would have a different set of values. He would be more empathetic towards animals and nature, seeing them as equals rather than something to be used. He would also be more solitary at first, but once he meets others, he would form very deep and loyal relationships as he values connection on a deeper level.
Harry Potter's personality would be drastically altered. Growing up with Azazel, he would lack the warm and nurturing environment that shaped the original Harry's kind - hearted nature. He might be more aloof and detached from others. Instead of being the hero who stands up for the weak, he could be more interested in using his power for his own gain. His sense of right and wrong would be blurred, influenced by Azazel's amoral ways, and he may not hesitate to use dark means to achieve his ends.
His personality would be much more calm and centered. Yoda's influence would make Harry less impulsive. He would think more before acting, which is a big change from the sometimes - rash Harry in the original books. He would also be more in touch with his emotions in a different way, not suppressing them but understanding their place in the grand scheme of things.
He might be more arrogant. Growing up with the Malfoys, he'd be used to thinking his family was superior. He'd lack the humility Harry in the original series has.