One of the many different trophies and achievements found within (TOCS4) Trails Of Cold Steel IV is Empty Chest-er.
Empty Chest-er requires players to find and open a total of 358 Treasure Chests. These Treasure Chests can be missed and found literally all over the place, hence why they can be missable.
They can usually be found within dungeons, towns and on the world map too.
One such location that features Treasure Chests is Saint-Gral Labyrinth (Phase 4) which features a total of 6 Treasure Chests all ripe for the taking.
SAINT-GRAL LABYRINTH (PHASE 4)
1) EP 3
2) Cast 3
3) U-Material x5
4) Flare Butterfly R
5) Sepith x50
6) Brave Seed