Here is the full list of all 28 AereA achievements.
Complete a sidequest
Complete the prologue
Retrieve the Accordion
Retrieve the Bagpipes
Retrieve the Baton
Retrieve the Bell
Retrieve the Drum
Retrieve the Lyre
Retrieve the Harp
Retrieve the Sousaphone
Retrieve the Violin
Reach level 10 with any class
Reach level 30 with any class
Reach level 50 with any class
Buy all skills from all classes
Upgrade all skills from all classes to level 3
Use a skill 100 times or more
Collect all shop books
Poison an enemy
Burn an enemy
Freeze an enemy
Hold 5.000 Clefines in your inventory
Hold 10.000 Clefines in your inventory
Hold 25.000 Clefines in your inventory
Complete 50% of all sidequests
Complete all sidequests
Play with 2-4 players
Revive a party member