Reformation of the World as Overseen by a Realist Demon King, Vol. 4 (manga)

Astaroth's winning combination of strategy and teamwork proves fatal for yet another demon king when Eligos falls before him! While Astaroth considers how to best utilize his new land, his people celebrate the victory as their king's fearsome reputation spreads throughout the realm. There's just one more order of business, though-summoning new allies to aid him in battle! What kind of powerful ally will join his ranks...?