The plot could start with Naruto encountering a strange entity that bestows the One for All power upon him. He then has to keep it a secret while he figures out how to use it. As he progresses, he discovers that there are others who are after this power, which leads to a series of battles and chases.
Perhaps in the fanfic, the One for All quirk could be linked to Naruto's Nine - Tails chakra. The two powerful forces could either clash or merge, creating a completely new power dynamic within Naruto. This could also cause internal struggles for Naruto as he tries to control both the wild nature of the Nine - Tails and the unique properties of One for All.
I'm not sure about a specific 'naruto has one for all fanfic' to recommend off - hand. You could try searching on fanfic websites like Archive of Our Own or FanFiction.net. There are likely some creative crossovers out there that combine the Naruto universe with the concept of One for All from My Hero Academia.
It would probably be really exciting. Naruto with the power of One for All could have some amazing new abilities. He might be able to use chakra in ways that are similar to how One for All is used in My Hero Academia, like enhancing his physical strength even more than he already can with his ninja skills.
A likely main character could be a young ninja who discovers he has the 'One for All' power. He would be on a journey to understand and control it, while also dealing with the normal challenges of being a ninja in the Naruto world, like training and making friends.
One interesting plotline could be the exploration of how the 'One for All' power from My Hero Academia would interact with the Naruto universe. For example, how a character with 'One for All' might face off against powerful ninjas. Maybe they use the power in unique ways during battles, like combining it with chakra-based jutsus.
If the All for One power was introduced to the Naruto universe, the power dynamics would be severely disrupted. Characters who were previously at the top in terms of power, like Naruto or Sasuke, would have to reevaluate their positions. The ability to steal and transfer powers would create a whole new level of threat.
One plot idea could be a character from the All for One world somehow ending up in the Naruto universe and having to adapt to the chakra system. Maybe they try to steal chakra powers like they steal quirks in their own world.
To create a compelling plot, think about how the different elements interact with each other. In the fanfic, Naruto could be on a quest to find the ultimate combination of all elements. Along the way, he meets different characters who each have their own relationship with a particular element, and they either help or hinder his progress. This creates a lot of conflict and drama. Also, the power dynamics between those who can control certain elements and those who can't can add depth to the story. For instance, a group of earth - style ninjas might be trying to hoard all the earth chakra sources, and Naruto has to stop them while also learning more about earth - style jutsu himself.
The students of UA High School would be really curious about Naruto's powers. Deku, for example, would probably be constantly asking Naruto about how his chakra works. And Naruto would be amazed by the Quirks of the heroes. He might try to figure out if there's a way to combine his jutsu with their Quirks.