To make it unique, focus on the power dynamics between them. Maybe the female shinigami has powers that Naruto doesn't understand at first, and he has to learn to work with her in a different way. And instead of a typical love - at - first - sight scenario, have their relationship develop slowly over many adventures. Have them argue and disagree on things like how to handle enemies, and then gradually come to understand and respect each other's viewpoints, which then leads to a deeper and more unique form of love.
You can make a Naruto noose fanfiction unique by changing the context of the noose. Instead of it being a normal noose, make it a noose made of chakra strings. This gives it a Naruto - like twist.
One unique feature is the blend of different power systems. Naruto has chakra - based powers, while Quincy have their spiritual bows and Shinigami have zanpakuto. In these fanfictions, seeing how these powers interact and combine is really interesting.
Well, in some fanfictions, the Shinigami might save Naruto by using its special powers to reverse a fatal curse or injury. For example, it could extract a harmful entity that was about to kill Naruto from his body.
Maybe the Shinigami uses its special powers to heal Naruto's severe injuries. For example, it could transfer some of its own spiritual energy to Naruto to revive his fading life force.
The shinigami's power over souls could be combined with Naruto's chakra. For example, Naruto could use his chakra to enhance the shinigami's ability to track lost souls in the Naruto world. Or the shinigami could use her soul - related powers to heal Naruto's chakra system when it's damaged. Maybe they could create a new jutsu that involves both chakra and soul manipulation, like a soul - chakra blast that can target an enemy's spiritual essence as well as their physical form.
To make a Naruto gender - swap fanfiction unique, you can change the character dynamics. For example, if Naruto is female, how does that change her relationship with Kakashi? Maybe Kakashi is more protective or has different training methods for her. Also, you can focus on different aspects of the ninja world that were not explored as much in the original. Such as the role of female ninjas in different clans.
To make the story unique, the author could focus on the relationship between Naruto and the female Kyuubi in a way that hasn't been explored before. For instance, instead of a typical master - servant relationship, they could have a more equal partnership where they learn from each other. The addition of Amaterasu could be used to create new power dynamics. Maybe the female Kyuubi has an unexpected reaction to Amaterasu that changes the course of the story.
To make a Futa Naruto and Kushina fanfiction unique, you could introduce new villains or challenges that are specifically related to Naruto's new form. For example, a villain who is after Naruto because of his unique futa powers. Another way is to create a different backstory for Naruto's transformation into a futa. Maybe it was a result of an ancient jutsu gone wrong.
A unique Naruto and Ghost Rider harem fanfiction can be created by focusing on character development. Develop Naruto and Ghost Rider's relationship in a way that's different from the norm. Maybe they start as rivals and then gradually become friends. For the harem, don't just focus on the romantic aspect. Have the harem members be involved in political intrigue or some sort of secret mission. This will make the fanfiction stand out as it weaves different elements together in an unexpected way.
Their first meeting could be really intense. Maybe Naruto is on a mission and stumbles upon a shinigami who is there for some unknown reason. Naruto, being curious, would approach the shinigami, and the shinigami, being a bit aloof at first, would be standoffish. But Naruto's charm would start to break through the shinigami's cold exterior.