Oj?sama S?sam? is based on the anime series Debutants Detective Corps, which tells the story of a group of young girls, led by the wealthy Ayanokouji sisters, which have received a threatening letter and decide to work as detectives to find out who has sent it. However, the game doesn't follow this story and instead puts the player into the shoes of a nameless male thief, whose goal is to outsmart the girls and to steal valuables successfully!

This is an adventure/puzzle game. The player navigates the thief through isometric locations. Each location typically contains dangerous spots that would deplete the thief's HP, and puzzles to solve, for example complex mazes with one-way-tiles. If the girls are close, the thief will hear a warning voice. Once a girl appears, it is possible to fight her in turn-based combat, but that requires weapons or other items, which should be found and which are not always readily accessible. If the hero's HP reaches zero, he is caught by the girls and put in prison.