The Overlord of Blood and Iron (WN) - Chapter 348: Kwak Jung Becomes a Vampire!

At 18, Alex Kain is whisked away to Eryndor, a game-like realm where he gains 'Skill Synthesis', a talent to fuse skills into godlike powers. Battling monsters and conquering dungeons, he builds a harem of strong women drawn to his might and charm. With the power to return to Earth bearing incredible resources, Alex faces a growing threat that endangers both worlds in this epic of adventure, romance, and ambition.

This is a world shrouded in darkness, and the pervasive black mist erodes all living beings.

Only fire can dispel the darkness and protect mankind.

But the firewood will eventually run out, the fire will eventually go out, and humanity will eventually perish.

until Rhodes came.

- Description from novelbuddy

In regards to the MMORPG Cross Reverie, Sakamoto Takuma boasted an overwhelming strength that was enough for him to be called the Demon King by the other players. One day, he gets summoned to another world with his appearance in the game. There, there are two people that insist “I am the real summon master.” Takuma gets slave-turning magic used for summoned beasts cast on him by the girls –

Beneath the peaceful façade of the modern world, an undercurrent of shocking crimes roils in the underbelly of society.