Unlockables, from the main menu:
Zelemir Skin - Changes Azra’s sprite to Zelemir in battles. Beat Normal Game to unlock this.
Sorceress Skin - Changes Azra’s sprite to the Sorceress in battles. Beat every sidequest to unlock this.
Music Box - Unlocked from the beginning. Allows playing any music track in the game as you encounter them.
Bestiary - Unlocked from the beginning. Shows new monster stats as you win levels that contain them.
Books:
Book of Loneliness - Only one of each unit type may be placed, but their stats are doubled.
Book of Blight - Dragonfire ceases to do damage, instead attempting to hit every enemy on the screen with each status effect, for a 25% chance per status effect.
World Map area:
Shrine of Fire - Sacrifice junk here to the Gods of the Flame in order to imbue each of your six main characters with a bonus aspect. Your Knight could take damage for an adjacent ally who would have died from the hit for 100,000 junk, or your archer could hide and go invisible once per battle for 10 seconds if she’s brought under 20% of max HP for, or your priest could gain a Martyr aspect that instantly heals all allies in it’s radius when killed and blinds all enemies.
A new ‘What if?’ bonus battle: Zelemir, Sorceress and the God-guy all on the far reaches of the map forming a triangle with Azra in the middle. All three must be taken down to win.