Madou Koukaku ~Yami no Tsuki Megami wa Doukoku de Utau~

Melkia empire is one of the five great countries in the middle of the continent, ruled by an emperor and four skilled field marshals. Its east provinces are constantly under attack from an old enemy, Yun Gasol alliance. When one of the four marshals dies in a battle, enraged emperor sends reinforcements to the region, and being a part of it Weisheit, the protagonist, now have to defend his homeland as a military commander.