I am unsure if these are all random drops or guaranteed or if they are difficulty specific but you need the following collectibles to unlock this story:
Forbidden - Blood Seal - dropped from the final boss. I got this as a part of my normal playthroughs
Origin of the Dragon's Reign - dropped from the Red Ink mini boss in chapter 2. She is the lady in the red dress that shoots laser and has some flying book adds. I got this as a part of my normal playthroughs
Sanhai Tome - Heluo - dropped from the boss at the end of chapter 3. I got this as a part of my normal playthroughs
Once you have all three go to the stand with the blue book at the beginning of the game and unlock the story for the achievement.