Another interesting approach is to focus on the origin of the Shiki Fujin in fanfiction. Maybe create a backstory where it was created by an ancient clan related to Naruto's Uzumaki heritage. This could open up new plotlines and mysteries.
In 'naruto uses shiki fujin fanfic', the story might focus on the consequences of Naruto using this powerful jutsu. It could explore how it affects his relationships with other characters. Since Shiki Fujin is a very dangerous and self - sacrificing jutsu, the fanfic could show how Naruto copes with the risks involved.
A possible plot could be that the devil fruit that Shiki has is a Logia - type devil fruit which allows him to turn into a certain substance. In the Naruto world, this confounds Naruto and his friends as they've never faced such an ability before. Shiki uses this power to infiltrate villages undetected. Naruto starts to study the nature of the devil fruit's power with the help of some of the more knowledgeable characters in the series, like Jiraiya (if he's still alive in this fanfiction). They eventually find a weakness in Shiki's power, which lies in a certain type of chakra that can disrupt the devil fruit's transformation process.
One possible plot twist could be that Naruto initially struggles a great deal with Shiki Fujin. Maybe he accidentally activates it in a wrong way and it starts to drain his chakra in an uncontrollable manner. This could lead to a situation where his friends have to step in to save him, and in the process, he discovers a new way to control the jutsu.
Well, one place to look could be on fanfiction.net. There are often a variety of Naruto - themed fanfics there, and you might be able to find some that involve Naruto using Shiki Fujin. Another option is Archive of Our Own (AO3). It has a large collection of fan - created works as well.
There could be a fanfiction where Naruto and Fujin go on a journey together to discover a lost ninja technique. Along the way, they face various challenges and their relationship grows as they learn to trust and rely on each other.
Incorporate unexpected twists. For instance, instead of the Shiki Fujin being a last - resort move, make it a move that has some unforeseen side effects that Naruto has to deal with throughout the story. This will keep the readers on their toes.
A really interesting plot could be a sort of 'what - if' scenario. For example, what if Shiki and Rima were to switch their roles or abilities? How would they adapt to this new situation? It could lead to some really creative storytelling, with them having to deal with the challenges and advantages that come with this role - reversal while still maintaining their bond.
Naruto's character could become more somber. Learning Shiki Fujin, a very dangerous and potentially self - sacrificing jutsu, might make him more aware of the weight of his responsibilities. He might start to think more about the consequences of his actions and be less impulsive.
One idea could be a story where Akira and Shiki are forced to team up against a new threat in the Togainu no Chi world. Maybe a powerful and mysterious figure emerges, and they have to put aside their differences to protect their territory.
In some fanfictions, Naruto Shiki might possess the power to manipulate shadow elements in extremely unique ways. For example, he could use his shadow to not only mimic the movements of others but also to create shadow constructs that can be used in combat, like shadow swords or shields.