The book could be about the history of the ninja clans. Maybe it contains long - lost secrets of the Uchiha or Senju clans. It might detail their ancient jutsus, alliances, and feuds.
Naruto's reaction would be a mix of curiosity and caution. He would be curious to explore the contents of the Bingo Book, looking at the profiles of different ninjas. However, he would also be cautious because he knows that having this book could make him a target. He might also feel a sense of responsibility, thinking that he has to protect the information in the book from falling into the wrong hands. He may even try to find out how the Bingo Book is updated and who is in charge of it, so that he can understand the system better and use it more effectively.
If the book contains powerful jutsu techniques, Naruto's combat abilities will improve. He might learn new ways to use his chakra or combine his existing jutsus in unexpected ways.
In this fanfiction, perhaps the ancient book leads Naruto on a new adventure. It could be that the book has a connection to an ancient clan, and Naruto has to uncover the truth about that clan while also dealing with the power or knowledge the book holds. For example, the book might have a map to a hidden place full of valuable resources or training opportunities. He would then have to figure out how to get there and what to do with what he finds.
Well, he might discover some interesting information about his enemies or other ninjas in the Bingo Book. Maybe he'll be shocked to find out details about certain characters he thought he knew.
One possible fanfiction could be about Kushina finding Naruto in a situation where he's lost in a forest. Maybe she uses her unique chakra sensing abilities to track him down. It could be a heartwarming story of a mother reuniting with her son.
One possible scenario in this fanfiction could be that Naruto discovers an ancient and mysterious shrine in the forest. The shrine might hold some sort of power or secret. Maybe it has a connection to the Sage of Six Paths. Naruto, being his curious self, would likely start to explore it. He might find strange markings or artifacts inside that he has never seen before.
Sasuke could be involved. He might be interested in the knowledge in the book too, and it could lead to some competition or cooperation between them. Maybe they need to work together to decipher the ancient text.