In a certain kingdom's capital, war is approaching. A young boy named Il, an apprentice guard, is treated as a useless person who can't do his job properly, living a lazy life while constantly relying on his stepsister. Amidst this, a certain “rumor” is spreading throughout the city. It is said that a mysterious group of assassins known as the “Nocturnal” are operating in the shadows. This is the story of the “worst” assassin among them. The dark hero of another world who slices through the night, brought to life by a popular original author and a new illustrator duo, makes his appearance here…!