Perhaps the One Ring could have an unexpected reaction to Naruto's chakra. It could either be attracted to it or repelled. This could create an interesting plot where Naruto has to deal with the power of the Ring while also trying to find a way back to his own world.
One possible plotline could be Arturia arriving in Middle - earth by some magical means. She might be mistaken for an elf at first due to her otherworldly appearance. Then, she could join the Fellowship on their journey, using her combat skills to protect them. Another plot could involve her being on a quest to find a powerful artifact in Middle - earth that has a connection to her own world.
One interesting story could be about Naruto finding the One Ring and having to resist its power with his ninja will. Maybe he teams up with Frodo and they teach each other about their respective worlds.
Fem Naruto could be a powerful ally in the Lord of the Rings fanfiction. She might use her ninja techniques to help protect the Fellowship. For instance, her chakra control could be used to sense danger or even heal wounds.
One way it could work is by having Naruto characters in Middle - earth. For example, Naruto with his shadow clone jutsu could be a great asset in the battles against Sauron's forces. He could create clones to confuse the orcs and trolls. Meanwhile, characters from 'Lord of the Rings' could learn from Naruto's ninja skills. Frodo might pick up some stealth techniques from Naruto's training.
Well, in some 'OC x The Lord of the Rings fanfiction', the OC could be an elf from a different part of Middle - earth that has a different culture and set of abilities. This OC might meet Legolas and they form a bond while sharing their respective elven knowledge. Also, there are fanfictions where the OC is a dwarf with a special talent for forging unique weapons that could potentially change the course of the war. And of course, there are stories where the OC is a human with a mysterious past that is somehow linked to the One Ring.
A fanfic could have Shirou befriending the hobbits. He could teach them some self - defense skills using his martial arts knowledge. And in return, the hobbits could introduce him to the simple joys of Shire life. Maybe he even helps them in their quest to destroy the One Ring in some way.
In a Dovahkiin x Lord of the Rings fanfiction, Dovahkiin could also explore the different cultures of Middle - earth. He might be intrigued by the elves' grace and knowledge. And his presence could potentially change the course of the war against Sauron. For instance, his dragon - riding skills could give the good guys an edge in aerial battles, if there were any in the story.
Perhaps some of the Hollows from Bleach escape into Middle - earth. The Fellowship of the Ring then has to team up with Soul Reapers who follow the Hollows there. The Soul Reapers could teach the Fellowship about the spiritual nature of the Hollows, and together they work out strategies to defeat them. For example, Aragorn could learn some combat techniques from the Soul Reapers, and in return, the Soul Reapers could gain knowledge about Middle - earth's geography and lore from Aragorn.
It can create a rift within the fandom. There are fans who appreciate the original work as it is and those who might be interested in such inappropriate fanfiction. This division can lead to arguments and a less - harmonious community. Also, it can discourage those who want to promote the positive aspects of the 'Lord of the Rings' series.