Senyuu.

A long time ago, a Demon King named Rchimedes brought chaos to the Human World before being sealed by the hero Creasion. A thousand years later, Rchimedes has returned, causing a rift that allows monsters to emerge. The King summons 75 likely descendants of Creasion to address the threat. The narrative centers on descendant number 45, Alba, and the royal soldier assigned to support him, Ross. The story includes an additional chapter beyond the main plot.