His sense of justice could be tested. Shego's powers are not always used for good in her original context. Naruto would have to make sure he uses these new powers in line with his ninja way. He could become more serious as he tries to control the darker aspects of Shego's powers, or he could use his own positive attitude to transform how those powers are perceived in the Naruto universe.
Naruto might become a bit more confident and cocky. Shego is often shown as self - assured, and having her powers could make Naruto feel more powerful. He might start showing off a bit more during battles.
His personality could be split. On one hand, he would still have his core values of heroism and kindness. But on the other hand, the dark quirk could bring out a more ruthless side. He might find himself having internal debates between using his power in a traditional heroic way or succumbing to the darker impulses that the quirk brings. This internal struggle would be a major part of his new personality in the fanfiction.
Naruto's personality would be a complex mix. On one hand, he might become more reserved due to Vader's influence. But on the other hand, his natural inclination towards goodness might cause him to constantly struggle against Vader's darker teachings. He could be a much more conflicted individual, with his usually open - hearted and friendly personality warped by the dark environment he was raised in. He might be more secretive and less trusting of others as well.
His core Naruto - like personality of being determined and never - giving - up would still be there. But he might become more refined and elegant like the elves. He would probably have more patience due to the elven influence. His boisterousness might be toned down a bit, but he would still be the energetic Naruto at heart, just with a more elven - like exterior in terms of behavior.
Naruto's personality might become more calm and centered. Yoda could teach him to control his impulsiveness. So instead of rushing into things, he'd think more before acting.
Naruto would likely be very conflicted. He is a person who values family deeply, so fighting his sister would go against his nature. This could make him seem more hesitant in the fight, constantly looking for a way to end it without hurting her too much.
Naruto might become more secretive. Growing up in the Snake Clan, which is often associated with secrecy and hidden motives, he could pick up on their ways of not revealing too much about himself or his plans. For instance, instead of being as open and brash as in the original series, he would be more guarded in his conversations.
Naruto might become more curious. Since he's reading about immortality, a concept quite different from his normal ninja life, he'll want to explore more about such ideas.
The OC's personality could also develop a sense of responsibility. Since the Goro Goro no Mi powers are so strong, they might feel a duty to use them for good. They could start to look out for the weak and oppressed in the world. For example, they might use their powers to protect a group of refugees from a corrupt government or a band of marauding pirates. They would understand that with great power comes great responsibility and strive to be a positive force in the world.
His powers would likely be used more for malevolent purposes. Instead of using his intangibility to avoid danger and protect others, he might use it to sneak up on people and startle or harm them.
Naruto's character would likely become more carefree. Luffy's powers often come with a sense of fun and adventure, and Naruto might adopt some of that. He'd be more likely to take risks and approach situations with a more light - hearted attitude.