In this fanfiction, female Naruto could be motivated by a sense of justice. She might think that Sasuke has been influenced by the wrong people or ideas, and by kidnapping him, she can re - educate him. She could believe that she can show him the true meaning of being a ninja, which is to protect the village and its people, rather than seeking power and revenge. This would create a conflict between Sasuke's existing beliefs and Naruto's new ideas, making for an interesting story.
One possible motive could be love. In the fanfiction, female Naruto might be secretly in love with Sasuke and sees kidnapping as a way to keep him close. Another motive could be to prevent Sasuke from seeking revenge. She may think that by kidnapping him, she can stop him from going down a dark path that will lead to his destruction.
Sasuke might want to get some information from Naruko. Maybe he suspects that she knows something about a threat to the Uchiha clan that he is trying to uncover.
One possible motive could be to use Sakura as bait. Maybe Sasuke is trying to lure Naruto to a certain location. He knows Naruto cares deeply about Sakura, so he figures Naruto will come after her.
One possible motive could be that Sasuke is being controlled by some dark force. Maybe an enemy has a hold over him and is using him to kidnap Sakura as a way to get to Naruto or the Hidden Leaf Village. Another reason might be a misunderstanding on Sasuke's part. He could think that Sakura has some information that is crucial to his personal vendetta and decides to take her by force to get that information.
One possible motive could be to protect Sasuke. Itachi might have seen a great danger approaching Sasuke that he could only avoid by taking him away forcefully. Maybe there was a powerful enemy targeting Sasuke, and Itachi thought that by kidnapping him, he could keep him safe in a hidden location and train him to become stronger.
Perhaps it's a personal grudge that Gaara has unknowingly held. Maybe there was an incident in the past where Naruto's actions had an indirect negative impact on someone Gaara cares about in Suna. Gaara's actions are often driven by his emotions and his past traumas. He could have bottled up this grudge without realizing it and finally decides to kidnap Naruto to get some sort of revenge or closure.
It might be for Naruto's own good. Sasuke may believe that Naruto is on a dangerous path that will lead to his downfall. So he captures him to keep him from making bad decisions, like sacrificing himself for the village or something similar. He wants to save Naruto from himself in a sense.
Shego might kidnap Kim Possible in fanfiction because of jealousy. Maybe Kim always gets the credit and Shego wants to show that she's just as capable. So, she kidnaps Kim to prove a point.
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 motive could be to use Naruto as a bargaining chip. Itachi was a complex character with his own goals related to the safety of the Hidden Leaf Village in some ways. He might have thought that by kidnapping Naruto, he could influence the village's decisions. For example, he could try to stop certain actions the village was planning that he believed would lead to more harm. Another motive could be related to the Nine - Tails within Naruto. Itachi might have wanted to study or control the power of the Nine - Tails for his own purposes, perhaps thinking it could be a way to protect Sasuke in a different manner.
One possible plotline could be that Sasuke has been misled by some false information. Maybe he believes that the female Naruto is in some way a threat to Konoha's future. So he kidnaps her to keep her away from the village. However, as he spends time with her, he realizes his mistake and they end up working together to clear up the misunderstanding.