Final Boss

When a Heroine game is created, one evil human is selected to be the game's Final Boss, the opponent the Protagonist must defeat in order to complete the game.

Overview
The people selected to become them had no good in them to begin with, and with their newfound powers the laws of their society no longer hold their desires in check anymore. Fortunately the Final Boss is sealed inside his personel fortress until the six Objective Bosses have been defeated, but he can still send out a very weak Avatar.

The Final Boss posesses tremendous power, more than enough to make every DeathSeeker submit to him, and level any city he desires. Still, his power is always inferior to the Demon Lords. For the sake of "balancing", whenever a Demon Lord is wounded or killed, the Final Boss receives a portion of that Demon Lord's power, depending on the damage.