Combatant No. 6, belonging to the secret society Kisaragi. As a vanguard of the evil organization, he has engaged in fierce battles with heroes until now, but the next place he's dispatched to is a fantasy world where swords and magic take center stage!?
Despite grumbling about the excessively black working environment, while searching for the thread of invasion with his partner, the beautiful android Alice (with a sharp tongue), it turns out that the species resembling humanity is under attack by the Demon King's army...
With no need for heroes anymore since they've already been surpassed by their peers, No. 6, now a mercenary, leads Snow (a money-grubber), Rose (the masochistic type), and Grim (the perpetually tardy) of the Royal Guard as they stand against the Demon King's army!