Here is the full list of all 16 Ys VI: The Ark of Napishtim achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Obtain every other achievement.
Defeat Majuunun.
Win the duel with Geis.
Win a boss fight with 1 HP remaining.
Complete Boss Rush mode on any difficulty.
Acquire every Tabulas.
Complete the game on Nightmare difficulty.
Complete the game in Catastrophe Mode.
Destroy the Ark’s Central Shaft.
Defeat Ernst.
Acquire all equipment.
Win a boss fight without taking a single hit.
Defeat Orjugan.
Defeat Ud-Meiyu.
Defeat Zonplas.
Defeat the Wandering Calamity.