Hazure Skill: The Guild Member with a Worthless Skill Is Actually a Legendary Assassin

Hazure Skill: The Guild Member with a Worthless Skill Is Actually a Legendary Assassin (外れスキル「影が薄い」を持つギルド職員が、実は伝説の暗殺者, Hazure Skill "Kage ga Usui" wo Motsu Guild Shokuin ga, Jitsu wa Densetsu no Ansatsusha) is an light novel series written by Kennoji and illustrated by KWKM. It has been licensed in English by Yen Press.

Plot
Roland is an assassin who, one day, breaks from his team and single-handedly "kills" the demon king. After returning to the kingdom, the king graciously promises Roland whatever he wants for his heroics. Conflicted in his desires—he hasn't thought of anything outside of killing for years—he remembers that one of his teammates told him what she plans to do after evil is defeated:

"Live an ordinary life."

And so Roland, with his ability to become unnoticeable and the disguised demon king/queen Laila at his side, decides to live a slow life.