Here is the full list of all 24 FINAL FANTASY achievements. It takes around 12-15 hours to unlock all of the achievements on Windows.
Gained titles of courage from Bahamut.
Collected treasure from 50% of the chests.
Restored the Fire Crystal's light.
Completed 50% of the Bestiary entries.
Restored the Earth Crystal's light.
Obtained 100,000 gil.
Obtained 50,000 gil.
Collected treasure from 10% of the chests.
Defeated 500 monsters.
Obtained 10,000 gil.
Defeated 300 monsters.
Played the 15 Puzzle game.
Completed 10% of the Bestiary entries.
Saved Princess Sarah by defeating Garland.
Defeated 100 monsters.
Earned all achievements.
Restored the Water Crystal's light.
Restored the Wind Crystal's light.
Defeated Chaos and restored peace to the world.
Obtained Excalibur.
Reached level 50 for all party members.
Completed 100% of the Bestiary entries.
Collected treasure from 100% of the chests.
Traveled to all the map locations.