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.
Forged a strong bond with Fie.
Forged a strong bond with Elliot.
Forged a strong bond with Machias.
Forged a strong bond with Jusis.
Forged a strong bond with Gaius.
Forged a strong bond with Kurt.
Forged a strong bond with Juna.
Forged a strong bond with Millium.
Completely filled the character section in the notebook.
Acquired over a million mira.
Used 100 S-Crafts in battle.
Completed the final chapter.
Completely filled the battle 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.
Achieved instructor rank S.
Collected all radio material and reported it to Munk.
Forged a strong bond with Emma.
Forged a strong bond with Sara.
Forged a strong bond with Altina.
Forged a strong bond with Alisa.
Forged a strong bond with Laura.
Forged a strong bond with Musse.
Forged a strong bond with Elise & Alfin.
Completely filled the fish section in the notebook. (All 25 types of fish + Rod Lv. Max)
Forged a strong bond with Ash.
Forged a strong bond with Towa.
Completely filled the recipe section in the notebook.
Took all landscape photos and reported them to Vivi.
Completely filled the cards section in the notebook.
Won 600 battles.
Completed Chapter 3.
Raised a master quartz to level 7.
Raised any two characters to Link Level 5.
Initiated 300 advantage encounters (including double and triple advantage).
Used Burst in battle 50 times.
Completed Chapter 2.
Used over 500 follow-up attacks in battle.
Used Rush in battle 100 times.
Inflicted Break over 800 times.
Used Brave Order in battle over 100 times.
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.