Here is the full list of all 39 Milo no Senki 3 achievements.
Finish the first chapter of Milo no Senki 3
Cross Hell's Gate
Defeat Disgaries
Reach the Isle of the Dead
Escape Hell with Nelson
Avoid spilling a thousand blood on the surface
Kickstart the Athermylian Great Wars
Do business with Shazoum
Call upon Thugs' greatest friend
Have Akilina reach level 20 before chapter 28
Reach level 20 with any character
Reach level 80 with any character
Eliminate a knight in one-hit using a mage
He clearly was not in another castle
Finish chapter 12 before Nelson arrives
Defeat all adversaries in chapter 27
Finish a chapter with only Milo alive
Finish chapter 16 selecting only Milo, Patrick, Quentin, Tâm, Vincent et Nelson
Finish chapter 30 selecting only Milo, Quentin, Kate, Jeremy, Kera et Jimmy
Complete the encyclopedia
Lose a character from a critical hit which was otherwise non-letal
Dodge a letal hit
Dodge 5 hits in a row in the same adversary turn using a Thug
Defeat 5 cavalrymen in the same adversary turn using Jimmy and Iauschi next to eachother
Defeat an archmage in one-hit without taking any damage
Finish chapter 20 selecting only Milo, Quentin, Kate, Arthur and Charles
Help Axel find his way
Tank a magical hit with Amira
Lose Patrick to a mage
Break a door with Kate or Quentin
Have Kate or Quentin broken by a door
Defeat a sniper with a cavalry unit
Defeat a mounted mage with Nolan
Defeat the mysterious scholar with Ester
Destroy an obelisk
Have Xuân as a Great Lord while Milo is still a Lord
Defeat an adversary in one-hit from 15 cells away
Defeat the three mysterious figthers in chapter 28
Defeat 5 adversaries, at least two of them armoured in the same adversary turn using Vincent