I'm not sure if there is an actual 'naruto kills his sister fanfic' specifically. But if there were, it would be a very twisted take on the Naruto universe. Naruto has always been shown to value family, even if he didn't have a traditional family growing up. He found family in his friends and in the village. So this idea of him killing his sister would be a radical departure from his core values.
The idea of a 'naruto kills his sister fanfic' is quite shocking. In the Naruto world, family bonds are important. Naruto's relationship with his father, for example, was revealed to be a complex and important part of his story. He also formed deep bonds with his friends who were like family to him. For him to kill his sister would mean a complete breakdown of the values that the series has built up over time. It's possible that in such a fanfic, there could be some sort of dark magic or mind control involved to make Naruto do such a thing, but it would still be very hard to justify within the context of the Naruto world.
One possible plot could be that Naruto is forced into a situation where he has no choice but to kill Haku in self - defense. Maybe Haku is under some kind of mind control and attacks Naruto relentlessly.
It could start with a rift between them that becomes unbridgeable. Sasuke might side with a group that Naruto is sworn to oppose. Their ideological differences grow to such an extent that they end up in a final battle. Naruto, with a heavy heart, kills Sasuke perhaps because Sasuke refuses to back down and his actions are endangering too many lives. This would be a tragic departure from the original story where their relationship was centered around mutual understanding and redemption.
There may be some fanfics out there with this disturbing concept, but it goes against the general nature of the Naruto series. One possible plotline could be that Naruto is somehow mind - controlled by an enemy and in that state, he attacks Hinata. But this is really a stretch as Naruto deeply cares for Hinata in the original series.
In the official 'Naruto' series, Naruto would never kill his family. However, in some extremely dark and non - canon fanfictions, such fanfictions might exist just for the shock value or to explore extreme 'what - if' scenarios. But this goes completely against the essence of Naruto's character, who values family and friends deeply.
If such a fanfiction exists, one possible reason could be a mind - control situation. Maybe an enemy uses some powerful genjutsu to make Naruto believe his sister is a threat, causing him to kill her accidentally. Another reason could be a misinformation plot where Naruto is tricked into thinking his sister has committed some unforgivable crime against the village.
One possible motive could be jealousy. Maybe she was jealous of Naruto's growing power and popularity within the village. Another reason might be related to some dark family secret or a curse that forces her to take his life against her will.
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.
In a 'Naruto abandoned for his sister' fanfic, perhaps there's a prophecy that only one of them can bring peace to the village. The elders, misinterpreting it, choose the sister and abandon Naruto. Naruto then goes on a journey outside the village, meets new friends and allies, and discovers new powers. Meanwhile, the sister is having her own struggles within the village, like dealing with the pressure of being the 'chosen one' and realizing that Naruto's abandonment might not have been fair.
Well, one possibility is that Naruto has to face a god - like being who is threatening the ninja world. Maybe this 'god' has been causing disasters or trying to enslave the people. Naruto, with his never - give - up attitude and powerful jutsu, finds a way to overcome the god's seemingly invincible powers. For example, he might tap into a new, deeper level of the Nine - Tails' chakra or combine the powers of his friends and allies in a unique way.
Most of the fandom would probably be horrified. Naruto is known for his positive values, and killing a family member is completely against that. There would likely be a lot of criticism towards the author of such a fanfic.