In the original Naruto canon, such a concept is completely against the established lore and is not possible. However, in the realm of fanfiction, while there might be some extremely out - there and non - canon ideas, I haven't come across one specifically with this plot. Fanfiction often has very creative and sometimes very strange ideas, but this one seems rather unorthodox and goes against the nature of the Nine - Tails as a powerful chakra - based entity, not a biological being in the traditional sense that can get pregnant.
In such a fanfiction, the plot might start with some ancient and dark jutsu that backfires on Naruto. As a result, the Nine - Tails gets pregnant. Naruto would be in a state of shock and confusion. He might seek help from the sages or other powerful ninja. Along the way, there could be those who want to use this situation for their own gain, while Naruto is trying to find a way to reverse the situation or accept it in a way that doesn't disrupt the balance of the ninja world.
It's extremely difficult. Given the nature of Naruto and the Nine - Tails in the original Naruto lore, it goes against so many established rules. However, if the writer is creative enough to create a whole new set of rules and explanations, perhaps it could be made somewhat believable. For example, by introducing a powerful and unknown entity that can manipulate the very essence of chakra in ways not known before.
Maybe through new jutsu or abilities. The fanfiction could give Naruto some unique power that allows him to communicate or negotiate with the Nine - Tails on a different level. He could use this power to show the Nine - Tails a different perspective, like the potential for harmony between them instead of constant struggle.
One interesting 'Naruto Gets Nine Tails' fanfiction could be where Naruto has an even deeper connection with the Nine - Tails than in the original series. For example, he can communicate with it telepathically without any chakra interference. Another one might be a fanfiction where Naruto uses the Nine - Tails' power in creative ways to solve problems that the original Naruto couldn't. Maybe he uses it to heal instead of just for combat.
Yes, in some fanfictions, Naruto is often depicted as having a very special connection to the Nine - Tails that goes beyond the normal relationship in the original story. For example, he might be able to fully control the Nine - Tails' power in ways not shown in the canon, or they could have a mental bond that allows for unique forms of communication and cooperation.
In some fanfiction concepts, the chakra of the Kyuubi is not just pure fox chakra but also contains remnants of the Sage of Six Paths' power. Since the Rinnegan is related to the Sage of Six Paths, when Naruto reaches a certain level of power and harmony with the Kyuubi, the dormant Rinnegan - like power within the Kyuubi's chakra awakens in Naruto. This could be a result of Naruto's strong will and his journey to master the Kyuubi's power which eventually leads to him obtaining the Rinnegan.
Well, in fanfiction, one could enhance the design of the Nine Tails Cloak by making it more adaptable. It could change its shape according to the situation. For instance, if Naruto is sneaking around, it could flatten and become more streamlined. Also, the color could shift slightly depending on his mood. If he's calm, it could be a lighter orange, and if he's enraged, a deeper red. Additionally, it could have some sort of aura or glow that gets stronger as he uses more of its power.
Another unique exploration could be through a shared goal that is not related to the main Naruto plot. For example, they both want to protect a special place in the spirit world that has significance for the Nine - Tails. To do this, they have to work together in a way that they haven't before. Naruto has to use his human skills and the Nine - Tails has to use its tailed - beast powers in harmony. This would show a different side of their relationship, one based on mutual respect for each other's abilities.
There are also some Naruto fanfiction communities on Tumblr. While it's not as organized as the other platforms in terms of a dedicated fanfiction library, you can still find some really good 'Naruto Gets Nine Tails' fanfictions through Tumblr blogs that are dedicated to Naruto fan content. You might have to do a bit more digging around, but it can be worth it as there are some unique stories there.