One interesting idea could be the exploration of Deku's powers from a new perspective. Since the character is reborn, perhaps they gain an enhanced understanding of One For All or develop new ways to use it more effectively. Another idea might be the relationships with other characters. The reborn Deku could form different bonds, like a closer friendship with Bakugo early on, changing the dynamics of their story.
Naruto's outgoing and boisterous personality would make Deku more confident. He would probably be more upfront and less shy. Naruto's strong sense of justice would also intensify Deku's already existing desire to help others.
In a fanfiction where Naruto is reborn as Deku, there would be a lot of potential for unique storylines. Naruto's experience with facing powerful enemies in the Naruto world could give Deku an edge. He might be more aggressive in battles compared to the original Deku. Also, Naruto's ability to make friends and form bonds could strengthen Deku's relationships with his classmates even further. And his understanding of power and how to grow stronger could lead to a faster development of Deku's abilities.
Obviously, Deku would be the main character since it's about being reborn as him. But other characters like All Might are also likely to be important. All Might was a huge influence on Deku in the original story, and in the fanfiction, he could still play a crucial role in mentoring the reborn Deku.
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.
In the manga, Deku experiences various ups and downs. He not only becomes stronger physically but also matures emotionally as he takes on greater responsibilities. There are also many unexpected plot twists that shape his journey.
It could lead to a completely different character dynamic and story arc. Maybe she'd face different challenges and have a unique perspective on being a hero.