Here is the full list of all 53 The Legend of Heroes: Trails of Cold Steel III achievements.
Mastered Trails of Cold Steel III and earned every achievement.
Completed the game on nightmare difficulty.
Opened every treasure chest.
Collected all radio material and reported it to Munk.
Completely filled the character section in the notebook.
Completely filled the books section in the notebook.
Completely filled the battle section in the notebook.
Initiated 300 advantage encounters (including double and triple advantage).
Used Brave Order in battle over 100 times.
Won 600 battles.
Used Rush in battle 100 times.
Completed the final chapter.
Achieved an academy grade of Prestigious.
Completed all quests, both at the branch campus and during field exercises.
Acquired over a million mira.
Gathered all 28 varieties of master quartz.
Completed Chapter 4.
Achieved instructor rank S.
Completely filled the fish section in the notebook. (All 25 types of fish + Rod Lv. Max)
Forged a strong bond with Fie.
Forged a strong bond with Sara.
Forged a strong bond with Gaius.
Forged a strong bond with Millium.
Forged a strong bond with Laura.
Forged a strong bond with Elise & Alfin.
Forged a strong bond with Machias.
Forged a strong bond with Emma.
Forged a strong bond with Elliot.
Forged a strong bond with Jusis.
Forged a strong bond with Towa.
Forged a strong bond with Alisa.
Forged a strong bond with Musse.
Forged a strong bond with Ash.
Forged a strong bond with Altina.
Forged a strong bond with Juna.
Forged a strong bond with Kurt.
Completely filled the recipe section in the notebook.
Completely filled the cards section in the notebook.
Took all landscape photos and reported them to Vivi.
Raised any two characters to Link Level 5.
Used Burst in battle 50 times.
Used over 500 follow-up attacks in battle.
Completed Chapter 3.
Raised a master quartz to level 7.
Completed Chapter 2.
Inflicted Break over 800 times.
Used 100 S-Crafts in battle.
Completed Chapter 1.
Earned an S-Rank on any chapter.
Won 100 battles.
Won a battle with a tactical bonus of x3.0 or greater.
Completed the prologue.
Completed the orienteering exercise.