Manga The Guild Official With The Out-Of-The-Way Skill “Shadowy” Is, In Fact, The Legendary Assassin

Roland is a killer who once breaks away from his team and "kills" the demon king alone (who is actually a girl because you already had to understand what the story is).

Returning to the kingdom, the king graciously promises Roland everything he wishes for his heroism. Contradictory desires - he had not thought about anything but murder for many years - he recalls how one of his teammates told him what she was going to do after evil was defeated:

Live a measured life.

And here Roland, with his ability to perfectly merge with the crowd and the disguised demon king Leila next to him, decides to live a peaceful life.