UNLOCKABLES

Entering the hidden dungeon, Kongokai
In the hidden dungeon, you can find the most powerful weapons in the game. You need to beat the game once and you must have a file saved before the final dungeon. From there, teleport to Shinjuku and head out to the world map. Once you are at the world map, head east and go to the NPC that's standing at the cliff side. He'll ask you whether or not you can go to Kongokai.