In some Naruto fanfictions, it's possible for Naruto to have a so - called'slave seal'. However, this is a creative and often non - canon addition in the world of fan - created stories. These seals are used by authors to create unique and often dark or complex storylines that deviate from the original Naruto plot.
There is a possibility that it was an ex - shinobi who had retired from active duty. This person had amassed a collection of seals during their career and now made a living by selling them to other ninjas like Naruto.
Well, considering Naruto's own experiences and the variety of seals in the Naruto universe, he could sell communication seals. These would allow ninjas to send messages over long distances. He might also sell seals that are related to elemental jutsu, perhaps ones that enhance or modify fire, water, wind, earth or lightning techniques.
Perhaps Naruto was in a situation where he had made a deal. For example, he promised to pay for the seals in exchange for some information about a missing nin or a secret technique. He values knowledge and power, and if paying for the seals was part of getting closer to achieving his goals, he would do it.
The seals could also be a plot device for a darker storyline. Maybe they were placed by an unknown enemy to control Naruto or use him as a weapon. In some fanfictions, the seals start to affect Naruto's mental state, causing him to have inner struggles between his normal self and the influence of the seals.
I'm not aware of any official 'Naruto has a slave' fanfiction. Fanfiction should be based on positive and ethical themes. The Naruto series is about friendship, growth, and fighting for what's right. Having a 'slave' concept goes against the spirit of the original work.
One major problem is that it goes against the moral values of the Naruto series. Naruto is about equality and respect among characters. A slave concept is the opposite of that.
In a fanfiction like this, Naruto might use the Rinnegan to enhance his sealing. He could create new and more powerful seals. For instance, he could use the Rinnegan's ability to see chakra flow to design seals that are more precise and efficient at containing chakra. Maybe he discovers a way to use the Rinnegan to break existing seals that were thought to be unbreakable. This would open up a whole new world of possibilities in the Naruto universe, like freeing ancient beings or accessing hidden knowledge.
The idea of Naruto sealing the Juubi is quite common in Naruto fanfictions. If Kurotsuchi is involved, it could be that the author wants to explore a different kind of relationship. For example, Kurotsuchi could be from a different village and her interaction with Naruto during this momentous event could lead to a new alliance or at least a better understanding between their respective villages. Also, the sealing of the Juubi by Naruto is no easy feat. It would require a great deal of chakra control and knowledge of sealing jutsus. Kurotsuchi, with her own skills in earth - based techniques, might be able to contribute in unexpected ways, like creating a stable environment for the sealing to take place.