Please Let Me Walk with the Devil!

The Demon King is a scourge of world destruction, an enemy of the gods, a taboo existence that brings endless fear and darkness, and is feared by all living creatures. But faced with such a demon king, the brave man who came to defeat him made such a request... "Onegai! If only you could not become the Demon King! Vadasi!" "How much awareness do you have when you say this? You are just a brave man. Can you shoulder the mission of the Demon King?" "... You brave man, you are really thinking about yourself." Under the sad gaze of the brave man, the Demon King turned and left. … Many years later, when the Demon King's heart is pierced by the sword of the hero, he will recall that distant afternoon when he first met the hero. —————— PS: This book is also known as "The Story of the Fall of the Brave Man", "The Development of the Demon King", "The Story of the Princess of the Restoration"... And so on.