Ochikobore Eishi Minarai no Shounen. (Jitsu wa) Saikyou Saiaku no Ansatsusha.

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 Night Dwellers are operating in the shadows.

This is the story of the worst assassin among them.

(Source: Ichijinsha, translated)