Robrave

Thirty years have passed since the hero sealed away the Demon King. The world seemed to have regained peace... but under the hero's leadership, the structure of society changed, and humans began to oppress and ruthlessly rule over "dwarves," "elves," and "ogres"—demi-humans. Demi-humans were treated as slaves, their dignity trampled upon day after day. In the midst of all this, the Demon King broke his seal and was resurrected! The epic counterattack of the demi-humans begins now!!

(Source: Kodansha, translated)

Note: Originally published as a one-shot under the title "Maou Douji (魔王童子)", was then picked up for serialization.