I really liked 'A New Beginning for Momoshiki in Naruto'. This fanfiction takes an interesting turn where Momoshiki is reincarnated in a different form and has to navigate the world of Naruto from a different perspective. It's full of action and also some great character development for Momoshiki. Also, 'Momoshiki and Naruto: Unlikely Allies' is a great read as it focuses on how their powers could combine in unexpected ways.
There are fanfictions where Momoshiki and Naruto interact in unique ways. Maybe Momoshiki has some knowledge that Naruto needs, and they have to negotiate. Their power levels are compared and contrasted. Naruto's ability to use Sage Mode and his chakra reserves are pitted against Momoshiki's alien - like powers. It creates a dynamic where both characters are forced to adapt to each other's fighting styles.
Yes, there are. You can find Naruto has Jougan fanfictions on various fanfiction platforms like FanFiction.net and Archive of Our Own. Just search for 'Naruto has Jougan' on their search bars.
One interesting concept could be the exploration of Naruto's new powers with the Jougan. Maybe he discovers hidden abilities that help him in battles he couldn't have won otherwise. For example, it could allow him to see through certain genjutsu more easily or sense chakra in a unique way.
Well, you could write a 'naruto jougan fanfic' where the main character has the Jougan but is initially afraid of its power. They could struggle with controlling it and accidentally cause some chaos in the village. As the story progresses, they learn to master it with the help of an old sage who has some knowledge about this rare dojutsu. This could lead to the character becoming a protector of the village in a new way, using the unique abilities of the Jougan.
There could be physical changes too. Naruto might have a new form that combines his own features with Momoshiki's. His body could become more resilient, like Momoshiki's, and he might have a different chakra signature. This new form could attract the attention of other villains in the Naruto universe, either out of fear or the desire to steal his power. Moreover, his relationships with other characters like Sasuke could be affected, as they have to adapt to this new Naruto who has absorbed Momoshiki.
For the ninja world in the fanfiction, it might bring a sense of peace as Momoshiki was a powerful threat. However, it could also lead to new enemies emerging, seeking revenge for Momoshiki's death. Naruto might also have to deal with the political fallout, as some villages might see his act as an overstep of power or a sign of aggression.
A Momoshiki fanfiction could focus on his relationship with Boruto in an alternate universe. For example, they could end up as allies instead of enemies. They might team up to face a greater threat that endangers both their worlds. This would involve a lot of character development for both of them as they learn to trust each other.