This trophy is obtained for completion of the first main story quest and is thus unmissable part of the progression through the game. Note this is the mission from the Adventurer's Guild NOT the tutorial/prologue mission which you will do when you first select your character.
**Minor Quest Spoilers Follow**
The onscreen text and narration will direct you to the next step of the main story quests every time you enter into town. To start off you will go to the adventurer guild and he will ask you to repair your items (on later characters you will skip this step). Return to the guildmaster after this and he will give you your mission (select the top option in the cutscene or else you cannot proceed), directing you to the 'Ancient Temple Ruins' (basically the first dungeon level). In the Ruins, proceed through the dungeon and fight the final Harpy boss. Once defeated, you will return to the adventurer's guild, but the mission is not yet complete - he will direct you to the temple in town to resurrect the bones that you recovered. Having done this, a final trip back to the adventurer's guild will complete the quest and earn you this trophy.