Here is the full list of all 33 Ys: The Oath in Felghana achievements.
Completed all other achievements.
Escorted Elena to safety on every difficulty level.
Escorted Christof to safety on every difficulty level.
Defeated the final boss without taking any damage.
Conquered Boss Rush on Nightmare.
Bested the master of the mountains in one-on-one combat.
Conquered Boss Rush on Hard.
Defeated "The Deadliest Cuteness."
Beat the game on Normal.
Beat the game on Hard.
Beat the game on Nightmare.
Beat the game on Inferno.
Achieved max level.
Beat the game in under 5 hours.
Beat the game on Easy.
"Measured" Elena.
Conquered Boss Rush on Normal.
Beat the game on Very Easy.
Maxed out all equipment.
Spent over 10 hours in a single playthrough.
Killed 500 Selnades across all playthroughs.
Killed 2,000 Mozgouz across all playthroughs.
"Killed" 50 immortal beasts without using the Silver Chimes.
Acquired every jewel.
Encountered every enemy in the game, excluding bosses.
Spoke with every character in the game at least once.
Defeated 5 or more enemies (except Mozgouz) at the same time.
Saved all of Hugo's pikkards.
Sold Randolph's ring to Cynthia.
Completed Anya's treasure-hunt game.
Died over 10 times on a single boss.
Enabled "No-Fall" mode.
Began the game on Very Easy.