She would likely become more resourceful. In Slytherin, she'd be surrounded by those who know how to use their surroundings to their advantage. So, Lily Luna might learn to be more cunning in getting what she wants, while still holding onto her moral compass from her family. For example, she could find clever ways to study for exams or solve mysteries around Hogwarts.
Lily Luna might develop a stronger sense of self - preservation. Slytherin values self - interest to an extent. This doesn't mean she'd become selfish, but rather she'd be more careful about the situations she gets into. She may also grow in her ability to read people, as Slytherins are often good at discerning motives. This would help her in her relationships, both friendly and otherwise.
In some fanfictions, Lily Luna Potter in Slytherin might be portrayed as an outcast within her own family's legacy. Since the Potters are mostly associated with Gryffindor, her being in Slytherin could make her feel like she has to prove herself more. She might be depicted as having a more cunning side, using her Slytherin traits to achieve her goals while still maintaining some of the Potter family's good - heartedness.
Their relationship could start as a simple acquaintance at Hogwarts. As they participate in school activities like Quidditch matches or wizard duels, they gradually become friends. Then, as they grow older, they might realize they have deeper feelings for each other.
His character would likely become more calculating. Instead of the impulsive Gryffindor actions, he'd think things through more carefully. For example, when facing challenges like the Triwizard Tournament, he might use his Slytherin traits to find loopholes in the rules rather than just charging in bravely.
He'd be more confident. With a loving mother around, he wouldn't have the insecurities that came from growing up with the Dursleys.
Well, it really depends on the fanfiction author's creativity. Some might give her a Patronus that reflects her own unique personality traits. For example, if she's portrayed as very brave and fierce in a particular fanfic, her Patronus could be a lioness, representing her courage and leadership. Another possibility is that it could be a bird, perhaps a phoenix, which would tie in with the magical and powerful nature often associated with the Potter family.
He'd be more cunning. In Gryffindor, Harry was brave and impulsive. In Slytherin, he'd learn to think before acting. He might also become more ambitious, not just about defeating Voldemort, but about changing the reputation of Slytherin.
Perhaps she forms an unlikely friendship with a pure - blood Slytherin who has very traditional views. Lily Luna tries to show this friend a different perspective on blood purity and the wizarding world in general. Their friendship causes a stir in the Slytherin common room, but they stick together through it all.
Naruto's character would likely become more calculating. He'd still have his core values of friendship and protecting his village, but he'd approach things with more cunning. For example, in battles, he might study his opponents' weaknesses more carefully before attacking. His social skills could also change. He might be more selective about who he trusts, using his Slytherin side to analyze people's motives.
His character would become more complex. He might start to question his Gryffindor - like instincts and develop a more calculating side. His confidence could take a hit initially as he tries to fit into a house with a different set of values.
His character would likely be more confident. Growing up with a loving mother like Lily, he wouldn't have the insecurities that came from the Dursleys' treatment.