Don't Come to Wendy's Flower House - Chapter 108

Gao Yang was an orphan who, at the age of six, crossed over to a “parallel world” and began living in a warm family of five.When he turned eighteen, Gao Yang accidentally discovered the truth about this world: it wasn't a parallel world at all, but a mysterious realm, and the loved ones and friends around him were all terrifying “Monsters”!Gao Yang, upon uncovering this truth, narrowly escaped death and, at a crucial moment, gained a system called “Luck” .The longer he survived, the stronger he became! And so, a deadly game of sheep and wolves unfolded...

Transform into Divine Dragon and dominate the world!
He is the only Divine Dragon in the sea who founded an underwater Dragon Palace.
With Crawfish Soldiers and Crab Generals as his followers, wild sharks and gigantic octopuses as his subordinates, he is the dragon that rules the city.

- Description from Novelupdates

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 –

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