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.
It could lead to some really interesting plot twists. Maybe Goku could prevent major disasters before they happen and change the course of events in the Dragon Ball universe.
In a Konoha 12 see the future fanfiction, many things could occur. They might see the destruction of Konoha and strive to prevent it. For example, Naruto could use his future knowledge to better train and unite the village. Sakura might focus on advancing her medical skills even further to deal with future threats. And Sasuke could use the knowledge to avoid certain paths that led to his past miseries.
Another possibility is that a new villain emerges as a result of the time - travel or whatever mechanism brings future Deku to the present. This villain could be from a future where Deku's actions (or inactions) have led to a more dangerous world, and he travels back in time to stop Deku from making those mistakes again. However, his methods are extreme and dangerous, making him the antagonist of the story.
Well, they might see a future where they have a big family. Since Naruto always wanted to be acknowledged and have people around him, he could see himself surrounded by his children and Hinata in a happy home. And for Hinata, she might see herself as a strong kunoichi, still supporting Naruto in his Hokage duties.
One possible plot could be that they see a future where the wizarding world is in great danger again. So they start to train young wizards secretly to prepare for the upcoming threat.
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.
If they saw the future, perhaps Naruto would see himself failing to save Sasuke. This could make him change his approach towards Sasuke, trying to understand his friend's pain more deeply and find a better way to bring him back to the right path. They might also foresee new and powerful enemies emerging, and start to search for allies or new jutsu to counter them.
A powerful vampire who also has some sort of mind - control ability could be the main antagonist. He might be trying to use Bella's future - seeing ability for his own evil purposes, like taking over the vampire world or destroying the werewolves.
Well, they could see the future through magical visions. Maybe a powerful sorcerer gives them a glimpse of what's to come. For example, they might see the rise of a new threat to Camelot or the discovery of a long - lost magical artifact that will change the fate of the kingdom.