His sister could actually act as a mediator between Naruto and Sasuke. She might understand both of their pain and goals better than they understand each other. So she could try to bring them closer, to make them see the good in each other again. For example, when Naruto and Sasuke have a fight, she could step in and make them talk things out instead of fighting.
If Naruto has a sister in the fanfiction, Sasuke might see her as another connection to Naruto. He could initially be suspicious of her, thinking she might be a liability to Naruto. But as time goes on, if she proves herself to be strong, Sasuke might respect her. Their relationship could also be a source of some jealousy for Sasuke, as Naruto might spend more time with his sister.
It could bring them closer. Having to learn and speak English together would mean they rely on each other more. They would share the struggles and the joys of mastering a new language, which would strengthen their bond.
Well, if Naruto has a twin sister, she might be more understanding towards Sasuke's pain. Unlike Naruto who sometimes challenges Sasuke head - on, she could approach him in a more empathetic way. Maybe she would be the one to first notice the changes in Sasuke after Itachi's visit and try to console him. This could lead to a different dynamic between Sasuke and the Uzumaki siblings, with Sasuke being more open to her than to Naruto at times.
Naruto would likely be very conflicted. He is a person who values family deeply, so fighting his sister would go against his nature. This could make him seem more hesitant in the fight, constantly looking for a way to end it without hurting her too much.
At first, Sasuke might not believe it was Naruto's own will. He would try to find out if Naruto was under some sort of external influence. But if he found out that Naruto was fully responsible, Sasuke's reaction would be one of pure hatred. He would abandon all his previous beliefs and goals and make it his sole mission to destroy Naruto. He might also cut off all ties with the village that Naruto was protecting, seeing it as an accomplice in his sister's death.
At first, their relationship might be a bit rocky. Naruto has grown up alone, and suddenly finding out he has a twin sister could be a shock. But as they get to know each other, they would start to rely on one another. For example, Naruto could protect Lemon in physical battles, while Lemon could offer him emotional support and advice.
His powers would likely be severely limited. The Sharingan, which requires a certain level of mental focus and chakra control, would probably not work as effectively. As a baby, Sasuke's chakra system is not fully developed, so he might not be able to access the full potential of his powers. He might only be able to use the Sharingan in short bursts, like when he's really scared or in immediate danger.
If Sasuke's sister was in the picture, Naruto and Sasuke's relationship might soften more quickly. Naruto would see another side of Sasuke through his sister. He might also feel more of a connection to Sasuke's family. Sasuke, on the other hand, would see Naruto's genuine care for his sister, which could make him trust Naruto more.
His sister might act as a mediator between Naruto and Sasuke. When they have their fall - outs, she could be the one to try and patch things up. She might see the potential in both of them and want them to work together for the good of the village.
His relationship with Sasuke would become more complex. Sasuke, who has always been proud of his Uchiha heritage and the Sharingan, might feel a mix of envy and pride that Naruto now has a part of what makes the Uchiha special. Naruto, on the other hand, would try to use the Sharingan to understand Sasuke better, perhaps seeing the world more from Sasuke's perspective.
The relationship could start with Naruto being overly protective of his sister, but she wants more independence. This causes friction. Later, when she gets into trouble that only Naruto can help her with, he steps in. This makes her realize that his over - protectiveness comes from love, and they begin to repair their relationship. For instance, if she is kidnapped by a powerful enemy, Naruto uses all his skills to rescue her, and during this process, they have heart - to - heart conversations.