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