Naruto might be initially confused. He trusts Tsunade, so being kidnapped by her would be completely unexpected. He would probably start by asking her why she's doing this.
Well, in general, any form of fanfiction that involves kidnapping and bondage themes can be a bit dicey in terms of ethics. In the Naruto universe, which is mainly aimed at a younger audience in its original form, such themes are far from the original intention. However, in the realm of fanfiction for an older and more mature audience who understand the fictional and consensual nature of such works in that context, it could be seen as a creative exploration of different scenarios. But it's important to note that it should always stay within the boundaries of legality and respect for the original source material.
In such a fanfiction, Naruto's friends would likely go on a desperate search for him. Sasuke might put aside his pride and team up with the others. They would follow any leads, like tracking the kidnapper's chakra signature if possible.
One possibility is that Naruto's friends launch a rescue mission. They would use their unique skills, like Sasuke's Sharingan or Sakura's medical ninjutsu combined with her combat skills, to find and save Naruto.
Well, it could be an obsessed fan who wants to keep Naruto all to themselves in the fanfiction. Maybe they think Naruto has some special power they can use for their own gain.
At first, Naruto would be stunned. But being Naruto, he'd quickly gather his wits. He'd probably joke around a bit to lighten the mood and try to get Hinata to open up. When he realizes she's serious, he'd start to analyze the situation. He'd think about what could have made Hinata do this and try to find a solution that would not only free him but also help Hinata if she's in some sort of trouble. He might also think about how this would affect their friends and the village as a whole.
Naruto could use his shadow clones. He might create a bunch of clones to distract Madara while he finds a way to break free from whatever is binding him. Since Madara is a powerful opponent, Naruto would need to be very strategic with his clone usage.
Another way Naruto could escape is by making an unexpected alliance. There might be other characters in the fanfiction who are also against Obito. Naruto could convince them to help him. For example, if there are some anti - Obito ninjas in the area, Naruto could appeal to their sense of justice and work together with them to escape.
Naruto could use his shadow clones to create a diversion. He might make a bunch of clones and have them attack the Akatsuki members in different directions while he tries to find a way out. For example, he could use the chaos to search for a hidden passage or a weak spot in their hideout.