An image generation system includes a processor including hardware, the processor being configured to implement: an object space setting process that performs a process that places a plurality of objects including a moving object in an object space; a moving object calculation process that performs a movement process that moves the moving object in the object space; and a parameter process that performs a process that sets at least one of an attack parameter, a defense parameter, and a movement control parameter of the moving object based on at least one of density information about an assemblage of particles within a line or a range that extends from the moving object in a given direction, and the density information about the assemblage of particles at a position of the moving object; and an image generation process that generates an image viewed from a given viewpoint in the object space.