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.
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.
Well, Naruto could potentially be used as a bargaining chip by Orochimaru. Orochimaru might try to trade Naruto for something he wants from Konoha, like secret jutsu scrolls or some kind of political power within the village. And Naruto, being the determined hero he is, would likely be constantly looking for a way to escape and foil Orochimaru's plans.
The story could start with Naruto being lured into a trap set by Kiri. Once kidnapped, he finds himself in a prison cell deep within Kiri's territory. The Kiri ninjas might try to interrogate him about Konoha's secrets or his own unique abilities. Naruto, being Naruto, refuses to cooperate. As time passes, he befriends a fellow captive who has some knowledge about Kiri's inner workings. With this new ally, Naruto formulates a plan to break free. Meanwhile, Konoha's search party is facing many obstacles in their attempt to find Naruto in the unfamiliar and dangerous land of Kiri.
It could be Orochimaru. He is always on the lookout for powerful specimens to experiment on or train in his ways. Naruto, as the son of the Fourth Hokage, would be an extremely appealing target for him at birth.