Abstract: Provided is a game system 1 that is a system for a game, the system having a plurality of information processing devices 10, the game including a story game and a battle game, battle presentation information with respect to terminal devices 10 of battle players of a battle in the battle game being calculated by using production information for the story game, and the battle being observable at a terminal device 10 of a battle-observation player, at least one of the information processing devices 10 including a battle-observation-presentation-information calculation unit 52 that calculates battle-observation presentation information with respect to the terminal device 10 of the battle-observation player of the battle on the basis of production information based on a progress level of the battle-observation player in the story game and input information related to the battle.