One interesting concept could be the power dynamics between Naruto and the Kyuubi in relation to doujutsu. Maybe Naruto gains a unique doujutsu ability because of his connection with the Kyuubi. For example, he could have a doujutsu that allows him to better control the Kyuubi's chakra or even see the memories of the Kyuubi's past hosts.
There could be original characters as well. In fanfiction, authors often create new characters to add to the story. For example, a new ninja from a hidden village who has a special doujutsu that somehow connects with the Kyuubi's power. This character could become an ally or an enemy to Naruto. They could bring in new plot elements, such as a new form of chakra that is only accessible through the combination of their doujutsu and the Kyuubi's power, which would make for a very exciting and unique story.
In 'naruto kyuubi doujutsu fanfiction', a cool concept is the potential for new jutsu creation. Since the Kyuubi is a powerful entity, the doujutsu could enable Naruto (assuming he has it) to combine his regular ninjutsu with the Kyuubi's power in novel ways. Maybe he could create a fire - based jutsu that has the added effect of draining the opponent's chakra, as the Kyuubi is known for its voracious chakra appetite. Also, the doujutsu might have a special mode for communication with other tailed beasts.
It could be a doujutsu that has the power of elemental control. For example, it could allow Naruto to manipulate fire or water chakra more effectively just by looking at it. This would be a great addition to his existing skills as he already has a large amount of chakra.
Naruto is usually a main character as he has a connection with the Kyuubi. Since he already has the Kyuubi sealed within him, it's logical that he would be the one to potentially unlock or develop the Kyuubi doujutsu. Sasuke might also be involved. His rivalry with Naruto could lead to interesting interactions in relation to the doujutsu, either trying to obtain it for himself or learning to counter it.
In fanfiction, the Naruto - Kyuubi pairing can greatly expand the power dynamics. For example, they might be able to defeat stronger enemies together more easily. It can also change the relationships Naruto has with other characters. If he has a closer bond with the Kyuubi, some characters might be more in awe or more fearful of him.
One popular Naruto Kyuubi pairing fanfiction could be 'The Bond of Jinchuriki'. It focuses on the unique relationship between Naruto and the Kyuubi, exploring how they gradually understand and support each other. Another is 'Kyuubi's New Perspective' which shows the story from the Kyuubi's point of view as it forms a deeper connection with Naruto. There's also 'Naruto and Kyuubi: United Front' where they team up against common enemies in ways not shown in the original series.
He would become more confident. Having a new and powerful ability would boost his self - assurance. He might be more willing to take on tougher opponents and challenges.
One possible power is the ability to see through illusions more easily. Since the Kyuubi is a powerful entity, a doujutsu from it could give Naruto an edge against genjutsu users. It could break through complex illusions that would otherwise trap him.
Another might be the Byakugan. It gives a wide - range view and can see the chakra points in the body. In fanfiction, new and unique abilities of these doujutsu can be explored. For example, the author might create a situation where the Sharingan can not only copy physical techniques but also mental jutsus.