Since the idea of one character becoming another's'slave' is not in line with positive values, it's not a good idea to promote or discuss such fanfiction in detail.
Some people might create such fanfiction out of a misinterpretation of the characters' relationships. They may want to explore extreme or 'edgy' scenarios without considering the ethical implications.
There might be some fanfictions with such a concept, but this is a rather unorthodox and not in line with the positive themes of the original Naruto series. In the original story, Kushina is Naruto's mother, and their relationship is based on family love and the greater Ninja world narrative.
Well, if Naruto becomes Mikoto, he would be a female in the body of Mikoto. He could bring his own values and experiences as Naruto. This could potentially change the relationship dynamics within the Uchiha clan. He may try to bridge the gap between the Uchiha and the rest of the village in a way that Mikoto might not have been able to do in the original story due to her own limitations and the circumstances of the time.
The story might be about how Mikoto, as Naruto's servant, helps him grow in power. She could train him in ways that the regular Konoha teachers can't. Since she comes from the Uchiha clan, she might have unique knowledge about chakra control and jutsu that she imparts to Naruto. Also, their relationship could develop from a master - servant dynamic to a deep friendship.
It's likely not one of the most popular concepts. Fanfiction often focuses on more positive relationships or exciting adventures. The idea of one character becoming another's slave has a lot of potential for misinterpretation and might not appeal to a large number of fans. However, there could be a niche group of fans who are interested in exploring the power dynamics and character growth that could come from such a situation.
If Naruto becomes Mikoto, it would likely change the events leading up to the Uchiha massacre. Naruto's strong sense of justice and his ability to make friends might prevent some of the animosity that led to that tragic event. He could use his influence within the clan to promote better relations with the village.
The relationship might change the power dynamics in the village. With Mikoto by Naruto's side, other clans might view Naruto differently. He would gain more respect and influence. Also, in battles, their combined strength could lead to quicker victories. Mikoto could also introduce Naruto to some of the Uchiha clan's secrets, which could be used to improve the village's defenses.
In this fanfiction scenario, Hanabi becoming Naruto's slave could also lead to some interesting character development for both. Naruto, who values freedom and friendship, might struggle with having someone in a subservient position to him. Hanabi, on the other hand, might initially resist but then grow to respect Naruto more deeply as she sees his good intentions and the things he can teach her.
In this fanfiction, perhaps there is an evil force that wants to use Anko to get to Naruto. By making Anko Naruto's slave, they hope to manipulate Naruto. But Naruto and Anko end up outsmarting the evil force. Naruto helps Anko regain her freedom and in the process, they both learn important lessons about friendship, trust and the value of freedom. Also, Anko might learn to respect Naruto more and Naruto might see a different side of Anko that he didn't before.