Marenian Tavern Story: Patty and the Hungry God

In order to unlock this, you'll need to accomplish a few tasks.

1) Encounter and defeat every monster and boss, including post game bosses.
This will require you to get the hammer from Heath after the main story has ended. Bellatina will ask you to retrieve a hammer from Heath at which point he will give you a weapon for Bellatina and a tool to break the large black rocks that have previously blocked your progress.

2) Collect all available drops from every monster.
Use Slashing Down (available for two or one handed swords) or a rune to increase drop rates.

3) Steal from every monster and boss.
Not to worry, if you don't steal from a particular boss during the story, there is a boss rush mode that unlocks after you beat the area bosses of White Cave. You do have to fight every boss and they are grouped, but it's not any real trouble if you can beat the regular bosses of White Cave. Just use a jewel to continue the fight, I had almost a hundred just sitting around by that point.

And that's it! You can check your progress from the Encyclopedia to see which monsters you are missing drops or steals from, and you can check each zone to see whether you are missing a monster by looking at the zone contents that show you what ingredients you can find there.

Please let me know if anything is inaccurate and I will be happy to update!