He could be resentful at first. After all, his parents have kept this big secret from him his whole life. But as he gets to know his twin, he might develop a sense of brotherly love. He may also start to question his family's values and actions in hiding his brother, which could lead to a change in his own character.
One possible reason could be to protect the family's reputation. Maybe the twin had some sort of condition or power that was considered abnormal in the wizarding world. Another reason might be for political gain or to avoid some sort of dark prophecy related to the twin.
At first, it could be strained. Draco, being used to being the only son in the family's eyes, might feel threatened by his twin. He could be jealous if his twin shows more magical talent or is more popular at Hogwarts. But as they grow older, they might start to understand each other better. For example, if they face a common enemy, like a bully from another house, they could come together and realize the importance of family.
The twin could change a lot. He might be the one who stops Draco from making some really bad decisions. For instance, if Draco was about to follow Voldemort's orders blindly, the twin could convince him otherwise. This would then change the whole course of Draco's actions and how he interacts with Harry Potter and his friends.
It could lead to all sorts of interesting plot twists. Maybe there's competition or a stronger bond between them.
Well, they could have a very complex relationship. On one hand, they might be extremely competitive, always trying to outdo each other in everything from academics to impressing their parents. Since they are in Slytherin, they could also team up and be a formidable duo, using their combined wits to get what they want in the wizarding world. Maybe they have a secret pact to protect each other no matter what.
Maybe it was a family secret to protect the twin from some dark force. Or perhaps there was a prophecy involved.
Maybe the twin brother has a special power that Draco doesn't. For example, he could be a seer like Trelawney but more accurate. His visions could show him the future of Hogwarts and the wizarding world during the dark times of Voldemort's return. He then tries to use this power to prevent bad things from happening, but Draco is suspicious of his actions and tries to stop him, thinking he's going against their family and the Dark Lord.
His brother could introduce new alliances. If he's more friendly or has different views from Draco, he might make friends with characters that Draco wouldn't usually associate with. This could lead to new storylines where Draco has to deal with these unexpected connections.
Well, first of all, his abilities should set him apart. He could have a natural talent for genjutsu, while Naruto struggles with it. His personality traits can be explored in relation to Naruto. If Naruto is the sunny optimist, the twin could be the brooding type, with a darker sense of humor. His relationships with the other villagers would also be a factor. He might not be as well - liked as Naruto at first, but as the story progresses, he earns their respect in his own way. Additionally, his reactions to Naruto's fame and how he carves out his own identity within the shinobi world are crucial for developing his character.
Well, in many such fanfictions, Harry might be shocked at first. He probably feels a sense of pity for Draco too. After all, being under the Imperius Curse means Draco has no control over his actions.