He might become more brooding and less open. Harry has always been a bit of an open book, but Vader's influence could make him more withdrawn as he contemplates power and the dark side.
Harry's personality could transform in multiple ways. Firstly, he could become more solitary. Instead of relying on his friends, he might think he can handle things alone like Vader. His confidence could turn into over - confidence. He may start to believe that he can control the fate of the wizarding world single - handedly. Also, his sense of morality could shift. He might not see the use of dark magic as completely unacceptable anymore. Instead, he might view it as a necessary means to an end, just as Vader uses the dark side of the Force for his goals, and this would be a huge departure from the Harry we know.
If it was a fanfiction like that, it would completely distort the perception of Harry Potter. Harry is a symbol of hope and light in his own universe, but if he was like Darth Vader, he'd be seen as a much darker and more menacing figure. As for Darth Vader, his iconic status as a Sith Lord might be diluted if his traits were randomly imposed on Harry Potter. It would be a very odd mash - up.
His personality would likely become more brooding. Darth Vader's influence might make Harry more withdrawn as he grapples with the new and often dark teachings. He may lose some of his innocence and optimism.
His personality might become more brooding. With Darth Vader's influence, Naruto could lose some of his naivete and become more cautious.
In this fanfiction scenario, Harry Potter's story would take a very dark turn. With Darth Vader as his guardian, Harry would be exposed to a world of power and control from a young age. He might not develop the same sense of justice and fairness as in the original story. Instead of fighting against Voldemort to protect the innocent, he could be more interested in ruling over the wizarding world. His magic might also be influenced by Vader's teachings, perhaps becoming more aggressive and less about helping others. His identity as a wizard would be overshadowed by his Vader - influenced upbringing, making him more of an outcast in the traditional wizarding society.
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.
In such a fanfiction, Harry Potter becoming a Darth Vader fan could lead to him adopting some of Vader's more authoritarian and decisive ways. He might start to use more forceful methods to deal with his enemies in the wizarding world, which would surely cause a stir among his friends and foes alike. For example, instead of relying solely on magic spells in a traditional way, he could be influenced by Vader's use of the Force and try to develop something similar in the magical realm.
His personality could become darker. Darth Vader's influence might make Naruto more brooding and less of the optimistic character he is. He could start to value power more than friendship at times.
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.
His personality could become more irreverent. Naruto is typically respectful of his elders and the ninja hierarchy, but Deadpool's influence might make him question and joke about those things more.