Isekai Kokka Alchimaira: Saijaku no Ou to Musou no Gunzei

Helian, the top player at the kingdom-management VR game called "Tactics Chronicles," was transported into the game world itself.
There he encountered a large army of demons running loose. And then there were the former NPCs, who have become the one-hundred-strong warlords. Helian hid his identity and set out on a quest with his vassals, only to find a tribe of elves who were being tormented by a giant malice. Seeing the tears of innocent people touched his heart, and he awakened to his true calling as a king. With righteous anger, he made up his mind.
With 100,000 demon troops under his banner, he will bring down the hammer with all his might on these atrocities!

"Rise up, my proud people!　Now is the time to respond with a roar!"

The thunderous roar that will shake the world, as his demon warriors march forward in unison with the mighty demon beasts known as archimera!

(Source: GA Bunko, translated)