In the fanfiction, it could be that Naruto inherits the doujutsu. There might be a hidden lineage that Naruto is a part of, and when the time is right, the doujutsu awakens within him. This could be related to his Uzumaki heritage, which has many secrets yet to be fully explored. It's possible that some long - lost relative had this doujutsu and it has been passed down through the generations, finally emerging in Naruto.
One possible doujutsu could be a time - manipulating doujutsu. It allows the user to slow down or speed up time in a small area, giving them an edge in battles. Another could be a soul - reading doujutsu, which enables the user to see the true intentions and past experiences of others by looking into their souls.
Well, in some fanfics, he might obtain them through some ancient ninja magic. Maybe he discovers a hidden scroll or a long - lost temple that grants him the power of all doujutsu.
Another possibility is that Naruto discovers some ancient and long - forgotten ninja art that allows him to either mimic or directly acquire the three doujutsu. It could be hidden in a secret scroll or a lost temple that he stumbles upon during one of his adventures. And this art gives him the ability to have all three doujutsu.
The doujutsu can drive the plot by giving characters unique powers. For example, if a character has a powerful doujutsu, it can make them a target for other characters who want to either steal the power or use it for their own purposes.
They might obtain new doujutsu powers through genetic experiments. In some fanfictions, evil scientists or rogue ninja might try to combine different bloodlines to create a new and powerful doujutsu. Another way is through a divine encounter. For example, a character could be blessed by a god - like entity in the Naruto universe and be given a new doujutsu power.
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.
The doujutsu might make Fem Naruto more empathetic towards Sasuke. For example, if it allows her to see his pain, she can respond in a more understanding way, which strengthens their bond.
The fanfiction where Naruto has all doujutsu has a huge impact on the Naruto universe. It alters the existing power hierarchy. Characters who were once threats may no longer be so. For instance, enemies like Pain or Madara might not be as formidable. Also, Naruto's relationships with his friends and mentors could change. His friends might look up to him even more, or some might feel left behind in terms of power. His mentors like Kakashi or Jiraiya might be surprised and have to adjust their training methods or expectations for him. Moreover, the story's overall theme of hard - earned growth through struggle could be diluted as Naruto's acquisition of all doujutsu could seem like an easy power - up.
The doujutsu from kami might also grant Naruto new offensive capabilities. It could potentially allow him to use some sort of energy projection or manipulation that is unique to this doujutsu. For example, he could fire beams of spiritual energy that can disrupt an opponent's chakra system.
It expands the Naruto universe by introducing new powers and abilities related to doujutsu. For example, new combinations of doujutsu that were not in the original series can be explored.