Kensen Hyōkyoku

Setsuka is the third imperial prince of Jan, a country that boasts great power. Aware that his chances of inheriting the throne was low due to his older brothers, he wishes to spend his days peacefully with his fiancée Shiraha, the daughter of the commander-in-chief, in a region where there will no longer be struggles for power. However, his hopes are dashed one day when the enemy nation pushes their invasion all the way to royal capital... These are the adventure records of Setsuka, the prince of a fallen nation.