Maoyuu Maou Yuusha

Fifteen years have passed since the war between humans and demons began.
These frequent battles between humans and demons have caused great suffering for everyone and general confusion.
In the midst of all this turmoil, a hero and his three companions found a way to bring victory to humankind.
But one day, the hero suddenly leaves his comrades-in-arms and goes alone to the Demon King's castle.
Our valiant warrior is welcomed by the Demon Queen, who makes him realize that humans need a common enemy to unite, but also to live better thanks to the economic development that war generates.
It is then that the two enemies decide to ally themselves to travel the land and see how to end the war, and above all, to decide if they should end it.