Perhaps Sasuke kidnaps female Naruto because he wants to protect her from a greater threat in his own way. He may not trust the others to keep her safe. He takes her to a secluded place. Naruto initially resists but then realizes Sasuke's intentions are not entirely malicious. They then start to have a conversation about their past and how things have changed between them.
It could be that Sasuke is being controlled by some dark force. This force makes him kidnap Naruto. Naruto, while kidnapped, tries to find a way to break the control over Sasuke. She uses her own chakra and their shared bond from their past to reach out to Sasuke's true self. Eventually, with her efforts, Sasuke starts to regain his senses little by little.
Well, it could start with Sasuke getting some false information that Sakura is being targeted by a powerful and evil organization. He decides to take matters into his own hands and kidnaps her to a secret location. Along the way, Sakura tries to escape, but as they encounter some of the real threats that Sasuke was worried about, she starts to understand his actions. They then team up to fight off the bad guys and in the process, their bond is reforged and they gain a new level of respect for each other.
Well, one possible plot could be that Sasuke has some sort of misunderstanding. Maybe he believes Naruto is in danger from an unseen enemy and kidnaps him to protect him. He takes Naruto to a secluded place, and at first Naruto is angry. But as they talk, they start to understand each other's motives better and their bond deepens.
Naruto could use her shadow clone jutsu. She could create multiple clones while Sasuke is distracted and then make her escape. Since she has a large amount of chakra, she can afford to create a lot of clones to confuse Sasuke.
One possible motive could be to force Naruto to understand his own power. Sasuke might think that by kidnapping Naruto, he can push Naruto to a situation where he has to tap into his full potential. Maybe Sasuke feels that Naruto has been relying too much on his friends and needs this shock to grow stronger on his own.
One possible plot could be that Sasuke has some misunderstanding. He might think Naruko is in danger from some hidden enemy in the village. So, he kidnaps her to protect her, but Naruko doesn't understand his intentions at first and struggles against him. Eventually, they start to communicate and Sasuke explains his reasons.
Perhaps Sasuke is being controlled by some dark force. He kidnaps the OC because the dark force wants to use the OC's special abilities. As the OC tries to reason with Sasuke, he gradually breaks free from the control and they end up teaming up against the real enemy.
Well, it could be that Sasuke has some ulterior motive like trying to get information from her. Maybe he believes Naruko has some knowledge about a threat to the village or to himself. He might be acting out of a sense of self - preservation or a misdirected attempt to protect others.
Perhaps Sakura kidnaps Sasuke because she suspects he is in danger from some unseen enemy. She believes that by taking him away from the normal routine, she can protect him. She might have some inside information about a threat to Sasuke's life. In the process, Sasuke at first is angry with her for this drastic measure, but then realizes her good intentions as she reveals what she knows.
Well, in this kind of fanfiction concept, it could be a very interesting plot twist. Naruto, being female, might have some strong motives for kidnapping Sasuke. Maybe she believes she can protect him better this way from the various threats in the Naruto world. It could also lead to a different kind of relationship development between them, far from the traditional friendship or rivalry.
Yes, there are many. You can search on fanfiction platforms like FanFiction.net or Archive of Our Own. Just add the keywords 'Naruto', 'Sasuke's sister' and exclude 'lemon' or any adult - related tags. There are often stories that focus on the relationship between Naruto, Sasuke and his sister in a more platonic or adventure - based way.