Humanity's Trust

Years passed, nothing happens humanity already lost 36% of its land and 20% of the human population.
The empress,Fei ruled the empire for already 4 years after her ancestors. But there is still no solution.
In a far enough land that would measure 6 kingdoms in total, there reside the huge empire of unknown and unclassified creatures.
The survivors described them as ferocious blood thirsty creatures known by the villagers,in legends,and from the rumors from the inner lands near the Great Palace,as Demons.
Leo never saw one demon, but feared them as he saw the corpse of his friends, brutally, mercilessly murdered.Leo was away during the attack of the demons assisting Her Majesty in new invented weapons.By that time he knew that humanity is nearing to extinction.Kai,is from the farmlands he saw the demons unlike Leo who is intelligent,Kai is simply someone desperate to survive and help those in need.
Astharoth is a squad leader at that time and soon became the general beside the empress