The Archives is a secret place that belongs to the Karibusa Family. It contains indespensible documents regarding mushi. They contain information on how to seal away mushi, and the various exploits of other Mushi Masters and their experiences with various types of Mushi.
But the documents itself arent the reason for the places' secrecy but it is the fact that The Forbidden Mushi have been sealed within the texts of these documents what makes it highly important.
The documents in the Archives are written by Scribes of the Karibusa family. Ever since the Forbidden Mushi was sealed into the Karibusa Family, every now and then a scribe is born. These archives are likely to be maintained until all the Forbidden Mushi in the Karibusa Family is sealed away in the documents.
As time progresses the paper gets old so the text needs to be copied into new scrolls to prevent the Forbidden Mushi from escaping.