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.
The OC could be a mysterious ninja from a far - off land. Sasuke might think this ninja has some secret knowledge about the Uchiha clan that he wants, so he kidnaps them.
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.
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, perhaps the plot of the fanfiction where Sasuke kidnaps the reader could involve a misunderstanding. Sasuke might think the reader is working for his enemies when in fact they are not. As for the story development, it could lead to the reader gradually understanding Sasuke's past traumas and reasons for his actions, and in the end, they might even help him heal some of his emotional wounds. And there could be a lot of action scenes where the reader tries to escape but then realizes that Sasuke is not really a bad guy in this situation.
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.
One possible plot could be that Sasuke has some sort of misunderstanding. Maybe he believes Sakura has some information about a threat to Konoha that she's not sharing, so he kidnaps her to force her to talk. Then Sakura tries to convince him that he's wrong while also trying to understand why Sasuke has become so extreme.
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.
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.
In some fanfictions, Sasuke could be under the influence of some dark power or curse. This power might compel him to kidnap Sakura. For example, a dark entity might want to use Sakura's abilities or her connection to Sasuke for its own evil purposes, and Sasuke, being unable to fully control himself, follows its commands.