Here is the full list of all 12 Celestial Hearts achievements.
Defeat the final boss on any difficulty.
Defeat the final boss on Hard difficulty or higher.
Emerge victorious in all five bouts in Vagrant's Arena.
Defeat Terminator Mk. III.
Defeat Hakutaku and Byakko.
Defeat Charybdis.
Defeat Strife.
Defeat the Zombie Yeti.
Defeat Seiryu.
Find Malady's Grimoire in The Depths.
Find ten secret areas.
Discover the true fate of Lilith.