Character Artwork - If you have acquired all of a certain character's voices, pressing square when highlighting their character in the Voice Collection screen will unlock their character artwork.
Seraphic Gate - You can unlock a bonus dungeon known as the Seraphic Gate by saving your game after the "Fin" screen at the end of the game. Then simply go to the main menu, and a new option to travel to Seraphic Gate will be available; you must use your clear data to do this.
-- Unlockables in the Seraphic Gate:
Each time you beat the Iseria Queen in Seraphic Gate, you receive a new chest and exp for your orb. However, if you beat it ten times you will receive an Angel Slayer, and each time thereafter will grant you another Angel Slayer and orb exp.
Tri-Emblem - Beat the Seraphic Gate once.
Book of Riddles 1-8 - Beat the Seraphic Gate 9 times, receiving one book each time through.