What was the easiest, simplest, most basic representation of 'Knowledge' that came to mind? For Eiro, it was a book.
Books were collections of knowledge, that which brought it to others, and that what brought it to Eiro in the past, and will continue to do so in the future. So, all of Eiro's knowledge was to be gathered within a single book in his mind to represent the ability
The memories that were missing were pages that had been ripped out or dirtied so that you weren't able to get the information from that page anymore. But no matter what Eiro tried, he wasn't able to properly make use of this book in the right way.
