BGM Test
Start the game in New Game +. BGM Test is now available in the game options.
Extra Chapter
Start the game in New Game +. After finishing the conversation with Cindy at the Dragon Tower before the prologue 1, the red orb in the dragon's mouth will be broken. Now you can access the extra chapter. However, the enemy here are very strong! Therefore, you should enter there once your characters are strong enough.
New Game +
Finish the game once, then select a slot to save. Next time, you can start a new game with all previously items, weapons and money.