Here is the full list of all 54 Ys IX: Monstrum Nox achievements. It takes around 50-60 hours to unlock all of the achievements on Windows.
Attain 100% of graffiti discovered.
Clear the Final Chapter.
Forge an Ultimate Armor.
Forge Ultimate Weapons for all Monstrums (6 in total).
Attain 100% of landmarks discovered.
Clear all Grimwald Nox.
Explore Balduq with the White Cat as leader.
Attain 100% of all "Materials" entries in your Journal.
Use Flash Guard 100 times.
Attain 100% of shops discovered.
Travel a total distance of 300 krimelye.
Clear Chapter 8.
Use Extra Skills 100 times.
Use Boost Mode 100 times.
Use Flash Move 100 times.
Clear Chapter 7.
Defeat 2,000 monsters.
Explore Balduq with the Doll as leader.
Clear Chapter 6.
Defeat 1,000 Lemures.
Clear Chapter 5.
Clear Chapter 4.
Clear Chapter 3.
Clear Chapter 2.
Achieve an S in a Grimwald Nox.
Clear the prologue.
Clear Chapter 1.
Begin your escape from the prison.
Finish "Balduq Prison" by Adol Christin in its entirety by earning all achievements.
Complete the map of Balduq.
Attain 100% of all treasure chests.
Attain 100% of all quests.
Attain 100% of all "People" entries in your Journal.
Attain 100% of all "Monsters" entries in your Journal.
Attain 100% of Affinity with all characters.
Attain 100% of Ritual Relics enhanced.
Attain 100% of Azure Petals found.
Have obtained a total of 2,000 NOX points.
Have 1,000,000 Gold in possession.
Unlock all 13 recipes at the Dandelion.
Reach max level with all skills.
Reach level 99 with any character.
Inflict Break 1,000 times.
Achieve an S on all Grimwald Nox.
Explore Balduq with the Crimson King as leader.
Explore Balduq with the Hawk as leader.
Explore Balduq with the Raging Bull as leader.
Explore Balduq with the Renegade as leader.
In Time Attack, defeat the boss in 30 seconds or less.
In Time Attack, defeat the boss without taking damage.
Complete Boss Rush.
Complete Boss Rush without retrying.
Clear the game on Nightmare difficulty or above.
Defeat the ultimate Lemures, Vakh Medios (excludes Time Attack).