The Empire of the Western Continent started an all out invasion against the states on the Eastern Continent.
Due to the strong weaponry, Emperor Otten III has unified the continent after several fierce battles.
But the Empire found itself in a weakened state as well.
Therefore, the elderly king decided that it is the duty of one of his sons to succeed to the throne.
His strategy: The first one who can give him a grandchild will inherit the throne.