Well, one possibility could be that Naruto is initially shocked to discover he has a sister. Maybe she was hidden away for some reason, like to protect her from the same threats Naruto faced as a Jinchuriki. They might bond over their shared family history and Naruto could finally have a real family connection that he always secretly longed for.
In a 'naruto meets his twin sister fanfiction', perhaps his sister has been living in a different village all this time. When they meet, she could be a very powerful ninja in her own right. Their meeting could stir up a lot of emotions, like Naruto feeling a sense of family he's never had before. They might team up to face a common enemy, using their shared bloodline abilities in unique ways.
Well, some of his friends could be really curious about his sister. They might start including her in their group activities. Naruto would then have to balance his time between his friends and his new - found family relationship with his sister. His friends might also learn a lot from his sister if she has some special skills or knowledge.
It could be someone who doesn't want Naruto and his sister to unite. Maybe a rogue ninja who fears their combined power. He might try to drive a wedge between them by spreading false rumors or causing misunderstandings.
In the Naruto series, Naruto doesn't have a biological sister in the original story. So in this fanfiction, the author probably creates a new character to be his sister. It could be an original character with unique abilities and a complex backstory that leads to the situation where Naruto dies by her hand.
The two main characters are Jon and his sister. Depending on the nature of the fanfiction, they could be very different in terms of character traits. One might be more outgoing while the other is more reserved. But the beauty of it is seeing how they interact and how their relationship unfolds when they meet.
It's possible that there is some sort of conflict at first. For example, they may have had a misunderstanding in the past that led to a rift between them. But as they meet, they start to clear up the confusion and gradually repair their relationship. This could involve apologies, explanations, and a newfound understanding of each other.
In the fanfiction, Goku might be initially shocked to meet his sister. He could then start to feel a strong sense of protectiveness towards her. Maybe they would train together to become stronger.
She could be an original character created specifically for this fanfiction. The author might give her unique abilities and a distinct personality to make the story more interesting.
One possible reason could be to protect her. Naruto might believe that by leaving, he can draw danger away from his sister. For example, if there are powerful enemies targeting him, he doesn't want his sister to get caught in the crossfire.