The Reformation of the World as Overseen by a Realist Demon King, Vol. 2 (manga) — Ryosuke Hata

With Astaroth's first victory under his belt, his rank as a demon king has increased, if only a little. Now that Sabnac and his castle are no more, Astaroth immediately sets himself apart from the rest of the demon kings with his new policies. Rejecting slavery and treating all his subjects as equals -- even the ones who had sworn fealty to Sabnac -- are just the start. Envisioning a grand city where humans and demons alike can live together in peace, Astaroth begins to put his plans to expand his territory into motion!