This is a very disturbing and inappropriate concept. In the official Naruto series, there is no such immoral content. Fanfics with such themes are not acceptable as they violate basic ethical and moral standards. We should focus on positive and healthy fan creations that are in line with the spirit of the original work.
Naruto would use his ninja skills. He might start with a diversion, like creating some clones to distract the assassin while he gets his sister to a safer place.
I'm not sure if there is such a specific fanfic. Fanfics cover a wide range of themes, but abuse within family in a Naruto fanfic might be a rather dark and not - so - common take. It could exist in some corners of the vast fanfic community, but it would also be quite controversial as Naruto is generally depicted in positive relationships in the original series.
Kiba could also be a good match. If Naruto's sister has an affinity for animals like he does, they could bond over their love for their respective animal companions. They could train together, and their combined skills with their animal partners could make them a formidable duo in battles and missions.
It could be due to a misunderstanding. Perhaps there was an incident where his sister was involved, but Naruto misinterpreted her actions as something malicious against him. Like she might have accidentally broken something precious of his and he thought it was on purpose.
There may be such fan - created works in some corners of the internet, but this kind of content goes against the general family - friendly and positive - value nature of the Naruto series. Naruto is mainly about friendship, growth, and the pursuit of dreams, and sexual content like this is not in line with the spirit of the original work.
Perhaps the story could start with Naruto finding out that his sister is in a secret location held captive by a dark organization. He embarks on a journey full of challenges. Along the way, he has to overcome various traps and face off against strong opponents. His shadow clones could play a crucial role in distracting the enemies while he reaches his sister. Once he does, he uses his chakra to break any bindings and brings her to safety, all while showing his growth as a ninja and a brother.
One common theme is self - discovery. Naruto's jealousy makes him look inward and realize his own insecurities. Another theme is family dynamics. It shows how jealousy can strain or strengthen the relationship between siblings and within the family. For example, Naruto might initially resent his sister but later learn to support her.
In this fanfic scenario, Naruto's character could take a darker turn. Maybe he becomes more solitary and distrustful. His sister, on the other hand, might be favored by Kushina but have her own internal struggles. The story could explore how Naruto overcomes his feelings of being abandoned and reconciles with his family.