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 would probably be really angry at first. He's a free - spirited person who doesn't like being forced into things. So he'd likely try to fight back right away, yelling at Sasuke about what he's doing.
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.
Good sasunaru mpreg fanfiction often has well - developed characters. It stays true to the personalities of Sasuke and Naruto from the original Naruto series. For example, Sasuke's brooding nature and Naruto's determination should be reflected.
One common theme is the exploration of family. Since Naruto is pregnant, there's a focus on how they will form a family, what kind of parents Sasuke and Naruto will be.
Another theme is unrequited friendship. Naruto sees Sasuke as his closest friend, but Sasuke's actions sometimes make Naruto feel like that friendship is not mutual, leading to hurt feelings. It's often about Naruto's struggle to hold on to that friendship in the face of Sasuke's coldness.
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.
Often, the theme of sacrifice is present. For example, one of them may have to sacrifice certain aspects of their ninja life to take care of the upcoming family. Also, the theme of family building is common. It shows how Naruto and Sasuke, who grew up without complete families in some ways, create their own family unit.
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.
Naruto would probably be very confused at first. He trusts Sasuke, even if it's a Fem Sasuke in this fanfiction, and he wouldn't expect to be kidnapped by her. So, his initial reaction might be to try and talk to her, asking her why she's doing this.