His personality might become more reserved. Growing up in the Malfoy household, he'd be surrounded by Slytherin values. So he could be more calculating and less impulsive compared to his original self. But he would still have that core of kindness from his parents.
In this fanfiction scenario, Harry's personality would be a blend of different factors. The Malfoy upbringing would likely make him more aware of appearances and social status. He'd be more polished in his speech and behavior. However, his experiences as an orphan and the knowledge of his parents' sacrifice would still be there. So he might be a bit more aloof on the surface but with a burning passion for the right things deep inside. He'd also have to deal with the expectations of the Malfoy family, which could either make him rebellious or force him to conform in some ways, all of which would shape a very different Harry Potter.
One possible plot could be that Harry grows up with a different perspective on the wizarding world. Narcissa might shield him from the more extreme pure - blood ideologies in her own family. He could still have his natural talent for magic but be trained in a more Slytherin - like way, focusing on cunning and self - preservation. And he might have a different relationship with Draco, perhaps more of a brotherly bond.
His magical abilities might develop in a different way. The Malfoys could introduce him to different types of magic or magical artifacts. Maybe he'd learn more about the Dark Arts in a different context, not for evil purposes but just to understand it better. He could also become more skilled in areas like Occlumency earlier on, since the Malfoys might see it as an important skill to protect their family secrets. His relationship with his Gryffindor traits would be tested. He might still have his bravery, but it could be expressed in different ways, like standing up to the Malfoy family's wrongdoings.
In some fanfictions, it starts with distrust. Harry sees Narcissa as part of the Malfoy family, which has been on the wrong side. But as the story progresses, they might find common ground, like protecting the wizarding world from a new threat. This makes them slowly build a reluctant partnership.
His life would change drastically. He'd be living in a different environment, with different values being pushed on him. Instead of the Dursleys' neglect, he'd face Lucius's attempts to mold him into a pure - blood - ideal wizard.
Harry's personality would be greatly influenced. He would be more polished in his behavior, as Narcissa would demand propriety. He might be less likely to take risks without thinking, as Narcissa would have instilled in him a sense of caution. His sense of loyalty would be more complex. Instead of the straightforward loyalty he has in the original story, it could be divided between Narcissa's family values and his own sense of right and wrong. Also, he may have a more aristocratic air about him, with a refined way of speaking and interacting with others.
Batman's brooding and serious personality would likely make Harry more cautious. Batman is all about planning and preparation, and Harry would pick up on that. For example, Harry might start to analyze magical situations more thoroughly before acting, instead of just relying on his instincts.
Loki's mischievous personality could make Harry more adventurous. Harry might start to take more risks in his magical studies and in facing Voldemort. For example, he could be more willing to try out untested spells or strategies.
Well, for Harry, he'd develop a deeper understanding of different kinds of magic and people. Since Tsuna comes from a different background, Harry would have to adapt his teaching methods. This would make him more flexible. Tsuna would start to develop a more adventurous spirit. He'd be more willing to take risks as he sees Harry's courage. Also, in terms of their relationship, they'd go from being strangers to a family - like unit. Tsuna would look up to Harry, and Harry would feel a need to protect Tsuna at all costs. This would shape their personalities in different ways, with Harry becoming more protective and Tsuna more trusting.
In such a fanfiction scenario, Harry might be exposed to a very different upbringing. Lucius could try to indoctrinate Harry with pure - blood supremacist ideas at first. But as time goes on, Harry's strong sense of justice might conflict with Lucius's beliefs. Maybe Harry would gradually change Lucius's view on Muggle - borns, or he could use his influence within the Malfoy family to bring about some positive changes in the wizarding world's view on blood purity.
Harry's personality would change significantly. Narcissa's influence would make him more secretive. He would learn to keep his cards close to his chest. Instead of being the open - hearted hero we know, he'd be more of a behind - the - scenes operator. His relationship with authority figures would also be different. He wouldn't be as quick to trust Dumbledore or other adults. He'd have a more cynical view of the wizarding world's power structures. His social skills would be more attuned to the Slytherin way of networking and manipulation, though he would still have his core of goodness that would lead him to oppose Voldemort in a different, more strategic way.