Well, Harry's personality would be a 180 - degree turn. He'd be more conniving and cruel. The Malfoys would have to adjust to having an 'evil' Harry in their family. Lucius might be more lenient with Harry's misdeeds compared to how he treated Draco. Draco would probably be jealous at times of the attention Harry gets from his parents. And the Hogwarts faculty would be very wary of Harry now. Dumbledore especially would be constantly trying to figure out how to 'save' Harry from his 'evil' path, while the Malfoys are trying to keep him on it.
Well, one possibility is that Harry, being 'evil' in this fic, might use the Malfoy family's wealth and influence to his advantage. He could learn dark magic from the Malfoys or their associates. Maybe he would turn against his old friends from Hogwarts and side with the Slytherin crowd more. He could also be involved in power struggles within the wizarding world, with the Malfoys backing him up.
His personality would likely be a blend of his natural Gryffindor traits and the influence of the Malfoy family. He might become more guarded and calculating at times, due to the Malfoy's sly nature. But his underlying sense of justice and loyalty would still shine through. For example, he might be more hesitant to trust people initially compared to in the original story.
In the 'Harry adopted by the Malfoys' fanfiction, one possibility is that Harry would receive a very different kind of magical education. The Malfoys might try to mold him into a Slytherin - like wizard, but Harry's own Gryffindor - like courage would constantly be at odds with that. Also, his relationship with Draco could be very complex, ranging from initial rivalry as they are brought up in the same household to a possible understanding and even friendship later on.
He might become more refined in his manners. The Malfoys are a very proper pure - blood family, so Harry would likely be taught to act more like them. For example, he'd probably have better table manners and a more sophisticated way of speaking.
Well, one possibility is that Harry would grow up with a very different set of values. The Malfoys are known for their pure - blood supremacist views. But perhaps, deep down, Harry could influence them to be a bit more accepting. He might learn dark magic quicker than in the original story, but also struggle with his own sense of right and wrong as the Malfoy values clash with what he feels inside.
Harry's character would be a blend of his original self and the Malfoy influence. He'd still have his innate sense of justice, but it might be expressed in a more Slytherin way. He could be more politically astute, understanding the power dynamics within the wizarding world better. And his relationship with magic would change. Instead of using it for pure altruistic reasons like before, he might use it to gain an edge in certain situations, at least in the beginning before he fully matures and reconciles his two different sides.
Obviously, Harry Potter is the central character. Then there are the Malfoys - Lucius, Narcissa, and Draco. Hermione and Ron might also be involved, perhaps as characters who are initially suspicious of Harry's new situation but later come to understand it.
If adopted by the Malfoys, Harry's personality would be a complex mix. He would be exposed to the Malfoy's elitist views from a young age. This could make him initially seem cold and distant. However, his innate goodness would still be there. He might struggle to reconcile his true self with the Malfoy persona he's expected to have. For example, he might be polite and proper in public as a Malfoy, but secretly help those who are oppressed by the pure - blood ideology, showing that his original kind - hearted personality is still fighting to surface.
He might be more reserved. The Malfoy upbringing would likely make him less impulsive compared to his canon self. He could also be more calculating in his actions.
Harry would likely be more confident in his pure - blood status, at least on the surface. Since he's raised by the Malfoys' twins, he'd be exposed to the pure - blood elitist culture from a young age. He might be more calculating and less impulsive than in the original story, having learned from the Malfoy family's shrewd ways.