Ougon no Keikenchi

The protagonist Leah, a girl who participated in the closed beta test of "Boot Hour, Shoot Curse", a new VRMMORPG that has no concept of levels or professions. Instead, players must farm experience points to gain new skills and increase their status.

Leah has acquired the hidden skill "Subordinate", which allows her to turn NPCs and monsters into her subordinates. The skill also transfers the experience points gained by the subordinates to herself. Continuously strengthening herself and her subordinates with accumulating experience points, she inadvertently received the classification of a Demon Lord...!?

(Source: Kadokawa, translated)