You might have to complete specific quests or challenges within the game to obtain Dios Diary. It could involve interacting with certain characters or exploring hidden areas.
Well, it depends on what you like. If you enjoy stories that are rooted in real events, it could be great. The fact that it's based on a true story gives it an authenticity that some fictional stories lack. It might show real - life situations, characters' struggles and triumphs in a more impactful way.