Shokei Sareta Kenja wa Lich ni Tensei Shite Shinryaku Sensou wo Hajimaru

The Sage Dwight along with the Hero defeated the Demon Lord who plunged the world into darkness. However, they were falsely accused of becoming the next Demon Lords because of their power, and were thrown to the Death Valley to die… Although his flesh had rotten away, he lived on as a skeleton because of his grudge against the world. Dwight has vowed to turn against that broken world, and with a power that surpasses even the former Demon King, and by leading countless Skeletons he's going to start an all out war…!

(Source: Comikey)