Well, Harry would likely be more confident. With Sirius around, he has a strong male figure who believes in him wholeheartedly. This would make Harry bolder in his actions and decisions.
His view of the wizarding world's authority might also change. Sirius has had his own run - ins with the Ministry. So, Harry, growing up with him, would be more likely to question the actions and motives of the Ministry and other powerful institutions in the wizarding world. This would make him more of a rebel in a way, but also more in tune with his own sense of right and wrong.
Harry would likely be more distrustful. Without the experience of having friends or family to rely on, he'd be hesitant to open up to new people. He may also be more independent in his decision - making, since he has no one to consult with. For example, he might not wait for others' opinions when facing a dangerous situation but just act according to his own judgment right away.
He likely becomes more confident. Growing up with the Weasleys, a large and loving family, gives him a sense of stability. He may not be as brooding as in the original series. For example, he might be more open about his feelings because he has so many siblings - like figures to talk to.
Snape could change by becoming more of a father figure to Harry. This would mean he'd be more protective and less likely to lash out with his usual sarcasm. He'd have to be more patient and understanding as he guides Harry through his magical education and the challenges of the wizarding world. This would also likely lead to him being more accepted by the other students and teachers as they see a different side of him.
It makes Harry more complex. He has to deal with the darker side of his new identity. He might become more reserved as he tries to figure out what it means to be the heir of Slytherin.
Sirius would have a big impact on Harry's understanding of family. Harry has always longed for a real family, and Sirius would show him what a loving and supportive family can be like. This would make Harry more open - hearted and less guarded. He would also be more likely to forgive those who have wronged him in the past, as Sirius might teach him the value of forgiveness. Moreover, Sirius' love for adventure could make Harry more adventurous in his exploration of magic and the wizarding world.
It changes his character development in that he becomes more distrustful. Since he has the Dark Mark, he might start to doubt the intentions of those around him. He might think that people will always suspect him, so he becomes more withdrawn. Also, his sense of self - identity is shaken. He's no longer just the Boy Who Lived, but now he's someone with a mark associated with the darkest of magic. This could lead to him exploring his own morality more deeply. He might question if he's doomed to be like Voldemort just because of this mark, and he has to fight against that internal struggle to define who he really is.
His character may become more self - reliant. Since he has to fend for himself in the forest, he learns to trust his own instincts. For instance, when facing a wild animal, he has to quickly decide whether to fight, flee or try to communicate with it.
Well, if Snape is Harry's godfather in the fanfiction, Harry might become more complex. He could inherit some of Snape's cynicism and guarded nature. Snape, being his godfather, would likely influence Harry's view of magic, perhaps making him more studious in potions and more attuned to the darker aspects of magic. This could also lead to a more conflicted Harry, as he has to balance Snape's teachings with what he learned from his friends at Hogwarts.
At first, Harry would likely be confused and scared. But this experience could force him to become more independent. He can't rely on Dumbledore or his friends at Hogwarts immediately. He has to learn to trust his own instincts and the bond he has with Sirius. This might make him more cautious in the future when it comes to trusting adults. For example, he might question Dumbledore's motives more often.
Well, it would likely make Harry feel extremely alone and betrayed. He already lost his parents, and Sirius was like a father figure. This could harden Harry, make him more distrustful, and he might become more self - reliant, not relying on others as much for emotional support.