This diary was no common diary one could buy at a local store. It was an artefact made with the concept of protecting the information stored in it with utmost security.
If not for Richard recognising its mechanism on time the diary would have been destroyed.
He fed his blood to the diary before the writings of his mother appeared.
Naturally, as a magic-infused diary, it had countless pages to provide a single space in which the user could store numerous memories.
And seeing the number of pages Richard had flipped, he knew his mother needed something like this.
Almost everything in the diary was related to Richard. His first footstep, to his first time speaking. Those sweet moments they spent together and how painful it was for her without him. Every single thing in details of everyday life which involved him were included in the diary.
