The Devil Is a Part-Timer!, Vol. 21 (manga)

THE DEVIL KING IS HIRING!In the heart of the Bluehorns- fortress, a young Satan confronts the enemy chief, Adramelech. Defeating him would mean adding the clan-s strength to Satan-s army, but the Bluehorns are merely one step on the road to uniting the demons under a single banner. Years later, Satan will be challenged by an even greater foe-Alciel, leader of the Iron Scorpions! How did the future Devil King meet his most loyal general?