One possible secret could be about Naruto's real parents' untold past. Maybe there are hidden details about how his father and mother met that were not in the original story.
It could be Naruto himself. As he grows and faces new challenges, he might stumble upon these secrets, either by accident or through his own determination to learn more about his world and his place in it.
Some fanfictions might reveal that Naruto has a secret relationship with a character that was not explored in the main story. For example, he could have a deep connection with a minor character from a different village, which changes the whole perspective of his character in terms of how he interacts with the ninja world.
One of the secrets could be about hidden relationships between characters. For example, a secret friendship that was never shown in the original books but explored in the fanfiction.
Well, one secret could be about the true origin of a certain character. Maybe in the fanfiction, it reveals that a side character has a much more important family lineage than was previously thought in the official Star Wars lore. For example, they might be related to a powerful Jedi or Sith from the past.
One secret could be about the true nature of certain magical artifacts that were only hinted at in the original books. For example, the Marauder's Map might have deeper secrets like how it was enchanted to show not just the castle but also hidden passages that lead to other magical realms.
Perhaps secrets about Madara's family. There could be old portraits or letters that show a different side of Madara. It might also reveal some of his early training methods.
It could also be Kakashi. There might be fanfictions where he has some secrets related to Naruto. For instance, he might be aware of a secret mission related to Naruto that he has been keeping from everyone, which could be a major plot point in the fanfiction.
One family secret story was about a hidden inheritance. A family had an old attic that no one really bothered with. But when they finally decided to clean it out, they found a box full of old letters and a deed to a small property that had been forgotten for generations. Turns out their great - grandfather had bought it but never told anyone. Another story is of a family that discovered they had a famous relative. A young girl was doing some genealogy research and found out that her great - aunt was a silent movie star. It was a huge shock as the family had no idea about this part of their history.
In the fanfiction, the scrolls could reveal a lot. For example, they might disclose the circumstances of Naruto's birth. Maybe there are prophecies written in them about Naruto's future. There could be stories of his parents' love and how they made sacrifices for the village and for Naruto. It could also be that the scrolls contain some sort of training method that was unique to his family, which would help Naruto become even stronger as a ninja.