Hazure Skill: The Guild Member with a Worthless Skill Is Actually a Legendary Assassin, Vol. 1 (light novel) — Kennoji

FROM HERO TO ZERO? Roland is the world's greatest assassin. With a seemingly worthless skill, he managed to kill the most powerful demon lord that's ever lived. He could easily spend the rest of his days as a wealthy and famous man. Such extravagance doesn't appeal much to Roland, however. He wants nothing more than an exceedingly normal life working at the Adventurers Guild, but such a unremarkable existence may not come effortlessly to someone so exceptional...