End Game Unlockables
Complete the game and save. Now there will be an extra 'bonus' option in the main menu. Doing the following will unlock the following modes in that menu. To access the extra 'Bonus' option in the 'Main' menu you must first successfully complete the game and save it. Then by completing the following tasks you can unlock the corresponding effect.

Unlock Gabriel Mode:
Maintain the radio that Gabriel and Xeride give you intact. When you are unsealing the swords only give signals to your GB until it gets a ! Mark.

Unlock Gunvard Revival:
In the village destroy ALL the marked objects.

Unlock Rabbit Battle Mode:
Complete the game then beat the Raging Rabbit.

Unlock Boss Battles Mode:
Complete the Monster Encyclopaedia

Unlock Summon Night 2 Battle Mode:
Get the highest Craftsmanship rank

Unlock Rival Battle Mode:
Complete the game

Unlock Sound Test Mode:
Complete ALL weapons