A brief description of the “The Guild Official With The Out-Of-The-Way Skill “Shadowy” Is, In Fact, The Legendary Assassin” manga:
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.