A player character appearing in a virtual game world is caused to perform actions in accordance with operation data. Based on the actions performed by the player character, operation tendency data, which indicates a tendency in operations performed by a player operating the player character, is generated, and a group of image data and the operation tendency data of the player character is stored. Then, an image of a non-player character indicated by the stored image data is displayed on a display device in accordance with the image data. An action of the non-player character in a virtual game world is controlled in accordance with the stored operation tendency data.