She could also be a love interest for one of Naruto's friends. This would create an interesting dynamic as Naruto would be caught in the middle of his friendship and his sister's relationship. For example, if she falls in love with Sasuke, Naruto would have to deal with the complications that arise from their relationship, while also trying to keep Sasuke on the right path.
She could be involved in the Akatsuki plot in some way. In the fanfiction, she might have been sent on a mission that led her to cross paths with the Akatsuki members. This could create a whole new storyline where Naruto has to rescue his sister from the clutches of the Akatsuki, adding more depth to the Naruto universe.
The older sister could act as a mentor. Since she's older, she might have more experience at Hogwarts and could guide Hermione through the social and academic aspects. For example, she could tell Hermione which professors are more lenient and which ones to be extra careful with.
The plot might revolve around the older sister being a part of a prophecy too. Just like Harry, she has a special destiny. But instead of being in the spotlight like Harry, she works behind the scenes to ensure Harry's success in the fight against Voldemort. She could be the one who finds out about Horcruxes first and guides Harry in that direction, all while dealing with her own challenges at Hogwarts, like trying to keep her identity as Harry's sister a secret from the wrong people.
She could play a protective role towards Harry. Since she's older, she might feel a strong sense of responsibility for her younger brother. For instance, she could be the one who first discovers some of the secrets about Voldemort's return and warns Harry.
Well, it could be about Kurenai taking on a sisterly role for Naruto. Maybe she helps him train, like teaching him some special genjutsu techniques that she's good at. She could also be there to support him emotionally, especially when he faces difficulties in the village or in his ninja missions.
If Maria's older sister existed in 'West Side Story', she could be a protector. She might try to keep Maria away from the dangerous gang - related situations. For example, she could stop Maria from seeing Tony if she thought it was too risky, considering the feud between the Jets and the Sharks.
She could be really shy. Growing up in Naruto's shadow, she might be hesitant to show her true self. Or she could be the opposite, very outgoing and confident, trying to make a name for herself separate from Naruto.
The baby sister could change Naruto in some ways. He might become more responsible and less reckless. He would have to think about her well - being all the time. For example, he might not take on as many dangerous missions so that he can be around to protect her. And as she grows up, she could also inspire Naruto to strive for a better future for the Hidden Leaf Village, not just for himself but for her as well.
She could be a half - blood like Harry. Maybe her mother was a muggle - born witch and her father was a pure - blood wizard. This mixed heritage could give her a unique perspective on the wizarding world's issues regarding blood purity.
One possible plot could be that Anko uses her skills and knowledge to protect Naruto from the very beginning. Since she's his sister, she might be more involved in his training at a younger age. Maybe she teaches him some of her unique jutsu privately, which gives Naruto an edge over his peers. For example, she could teach him some of her snake - related jutsu, which Naruto could then modify to fit his own style.