Genjitsu Shugi Yuusha no Oukoku Saikenki

Synopsis

In an alternate world, King Albert of Elfrieden and Prime Minister Marx decide to summon a hero to face a dire threat. Kazuya Souma, a young man training to be a civil servant, finds himself summoned as their hero. Albert and Marx explain demons appeared 10 years ago and took over the northern kingdoms. The remaining kingdoms keep them invading, but maintaining armies is expensive, so Kazuya was summoned by the bankrupt Elfrieden Kingdom to trade to the Gran-Chaos Kingdom instead of gold. Kazuya convinces Albert to keep him as he was training to be a civil servant. For three days, Kazuya learns everything he can about Elfreiden's economy. On the fourth day, Albert announces he is abdicating the throne to a shocked Kazuya, who will also marry his daughter, Liscia. Liscia is convinced Kazuya stole the kingdom, but is surprised to find he has already found the money for Gran-Chaos by trading Elfrieden jewelry to the neighboring Amidonia Principality. Liscia realizes his other plans are also well thought out. Elsewhere, Duchess Excel of Walter sends her granddaughter Canaria to spy on Kazuya and decide if he is as capable as he appears.

(Source: Wikipedia)