The Prologue:

Once Upon a Time, medieval folktale speaks of a cursed "S" class Knight whos reputation stretched far and wide.

It was from his battle with a Class 3 Witch  that he  received his curse! 

Just before decapitation; the witch used her last dying words to place a hex upon the knight! Bounding him with a demon! The only way the curse is lifted is if the knight shall perish.

Since that day, the Knight wanders from place to place selling his services to banish  evil. 

The knights name of this tale is  Henry; The knight of Demons and This is a tale of one of his adventures.