Every child of the land has heard of that bedtime story.
The tale of The Undying Flame inside forgotten ruins, waiting for someone brave enough to lay a hand on it. About the monsters that were sealed alongside The Flame, and how not a single soul ever returned with their prize.

Every thief of the land have made it their goal, and they, The Lustrous Blank, are the greatest pretenders to the ultimate treasure.
And yet, what lies in wait beyond the gate is no treasure nor monsters, but the entry to the realm of an absolute conqueror, where The Overlord waits for someone to shoulder the fate of humanity.