Harry's confidence would likely grow in a different way. Instead of the boy - who - lived bravado, he'd have a more quiet and self - assured confidence. He'd know that he has powers and knowledge that others don't, and this would show in his demeanor. He might be less impulsive and more calculating, which could both help and hinder his relationships and his ability to protect the wizarding world.
He might become more brooding. The need to control his bloodlust could make him withdrawn.
He might become more authoritative. Since he has the power of an emperor, he would need to make tough decisions and be more assertive in his commands.
He might become more stealthy and reserved. Instead of being as open as he was in the wizarding world, he'd have to be more secretive as a ninja.
Well, he might gain new and mysterious powers. The Grey Lords often have a complex relationship with magic, so Harry could find himself delving into darker or more ambiguous forms of magic. Maybe he'd use this new power to change the wizarding world in unexpected ways, like reforming the Ministry of Magic's policies regarding dark creatures.
His sense of responsibility would likely increase even more. Harry has always been responsible, but as a priest, he would feel accountable for the spiritual well - being of others. He would become more solemn and less impulsive perhaps. His Gryffindor impulsiveness might be toned down as he takes on a more serious religious role.
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.
He would become more rebellious. Harry has always had a bit of a rebellious streak in the original series, but as a pirate, it would be amplified. He'd be more likely to question authority and do things his own way without waiting for permission.
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.