Idle Big Devil

Humans, Demons, Elves and Undead coexist peacefully on the same continent until the balance was broken: A fallen prince of the human kingdom accepted the contract with Undead, and evil spirits arose from the hell to cloud the minds of most creatures.

In such a critical situation, you are appointed by the King as a new lord with the duty to gather new heroes to fight against the darkness.
One of the elders secretly tell you a secret that the energy of heroes can be combined.
And the High Priest creates a device to duplicate heroes. All duplicates have no feelings or minds.
With all these, you are going to prepare yourself for monsters, fallen heroes, and other competitive lords.