If Deku had a quirk in fanfiction, it would likely impact his character development. He might have become more powerful quicker or taken on different enemies. The story could become much more action-packed or focus on different themes.
It could have completely changed the dynamics of his battles and his relationships with others. The Sharingan would have given him an extra edge and new abilities.
It could make for a really exciting and unique story. Deku's growth and challenges would be measured in a more structured way, adding a new layer of excitement to his journey.
If Naruto had the Sharingan in fanfic, he'd likely become even more powerful. His combat skills would improve as he could use the Sharingan to predict his opponents' moves more accurately. He might also be able to use some of the unique jutsus associated with the Sharingan. For example, he could potentially learn to use Amaterasu if the fanfic writer allows for that kind of power combination.
In a fanfic, Naruto with the Rinnegan and Sharingan would have a whole new set of challenges. He would have to deal with the jealousy and fear of other ninja villages. His own village might also be divided on how to handle his new powers. On the positive side, he could use these eyes to better understand the history of the ninja world. For example, the Rinnegan might give him insights into the Sage of Six Paths' true intentions, and the Sharingan could help him uncover secrets about his own family. He would also have to train hard to fully utilize the combined potential of these two powerful eyes, which could lead to some interesting training arcs in the fanfic.
Well, he'd probably be extremely powerful. The Sharingan already gives some great abilities like enhanced perception and the ability to copy jutsu. If Naruto had a blue Sharingan, he might be able to combine those with his own massive chakra reserves. Maybe he could use the Sharingan to better understand and counter his opponents' moves while using his Rasengan or other jutsu more effectively.
In 'deku meets future deku fanfiction', perhaps the future Deku warns the present one about upcoming threats. He could tell him about villains he'll face in the future and how to defeat them. This would give the present Deku an edge in his battles and also in his growth as a hero.
One possible plot could be that Villain Deku is on a mission to undermine the hero society and crosses paths with Hero Deku. They engage in a fierce battle where Villain Deku taunts Hero Deku about his ideals. In the end, Hero Deku manages to get through to a small part of Villain Deku's conscience, leaving him with some doubts about his villainous path.
Another plot might involve the older Deku being from an alternate timeline. He shows the younger Deku different ways he could have developed his skills and relationships, which makes the younger Deku reevaluate his own path as a hero.