His confidence would likely soar. Naruto has always been confident, but as the Sorcerer Supreme, he'd have an even greater sense of self - assurance. He'd know he has the power to protect and make a difference on a much larger scale. He might also become more reserved in some ways, as he'd have to deal with more serious magical matters and might not be as quick to jump into action without thinking first.
His confidence might increase even more. Naruto was always confident as a ninja, but as a sorcerer, he has new powers at his disposal. He would feel even more capable of taking on challenges. For example, if he faces a powerful sorcerer enemy, instead of being intimidated, he would be eager to test his new abilities.
Well, Naruto's personality would have an interesting transformation. He would likely become more of a risk - taker. The pirate world is full of uncertainties and dangers, and Naruto would embrace this. He might become more laid - back in some ways, enjoying the simple pleasures of life at sea like drinking grog (if they have something similar in this fanfiction world) and singing sea shanties. But at the same time, his competitive nature would still be there. He'd want to prove himself as a great pirate, perhaps competing with other well - known pirates. His naivete might also change a bit. While he was often naive in the ninja world, the harshness of the pirate life would make him more street - smart, yet still retain his positive outlook on life.
If Naruto becomes the Sorcerer Supreme in fanfiction, he would likely combine his ninja skills with powerful magic. He could use his Rasengan with magical enhancements, making it even more destructive. His shadow clone jutsu might also take on a new form, perhaps being able to duplicate magical powers as well. Naruto's strong sense of justice would be amplified in this new role, and he would probably use his position to protect the ninja world and the magical realm from any threats that might emerge.
He might become more brooding. The new powers and the vampiric nature could make him a bit more withdrawn as he tries to understand and control his abilities. But his core of kindness would still be there.
Naruto's personality could become more complex. He was always an optimist as a ninja, but as a shinigami, he might see the darker side of things more often. However, his core values of friendship and protecting others would remain. He might be a bit more reserved in expressing his emotions as the shinigami world may have different social norms. But overall, he'd still be the same Naruto at heart, just with a different perspective on life and death.
He might become more patient. Blacksmithing requires a great deal of patience, and this could seep into his personality. He would have to be meticulous in his work, which could make him more detail - oriented in his interactions with others as well.
His already positive personality would become even more so. He'd be like a beacon of hope. He might be more focused on bringing out the best in others, since that's what Blue Lanterns do.
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.
If Naruto becomes involved with Slenderman in a fanfiction, his usually cheerful and determined personality might become darker. He could be more withdrawn as he grapples with the strange and often terrifying aspects of Slenderman's world.