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.
One of the great Danmachi fanfics is 'A Different Perspective'. It offers a fresh take on the characters and their relationships within the Danmachi universe. The story delves deeper into the backstories of some minor characters and makes them more significant. Another good one is 'The Unseen Adventures'. It takes the characters on new quests that are not in the original story, adding more excitement and mystery.
The Danmachi light novel is finished. The author completed the series, providing a satisfying conclusion to the adventures and developments of the characters.