Genjitsushugi Yuusha no Oukoku Saikenki

In a world where the Demon King had taken over a fifth of the land. Souma Kazuya (Soma) was summoned to that world as a hero, but the king took a liking to his rich country strong army proposal and somehow handed him the throne. Soma, who had the throne forced upon him, forewent adventure, and together with the talented companions he gathered, went about his nation-building with his realism.