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