We present a novel framework for simulating time-varying decay effects for natural images. Conventional methods assume the input image includes enough decay information and uses the color or texture information of the decayed regions to transfer its effect to the non-decayed regions. Unlike these approaches, our framework generates diverse patterns of decay effects by leveraging a decay effects generator network without referencing the decay features of the input image, which allows us to handle more general images with non-decayed objects. Our decay generator network is formed by a style-based generative adversarial network with an arbitrary-sized stationary texture generation mechanism that allows us to synthesize various sizes of decay textures. This arbitrary-sized stationary texture generation is necessary to synthesize photo-realistic decay effects since the appropriate resolutions of the decay textures depend on those of the target objects. We construct a novel decay texture image dataset that contains various types of decay texture images, such as mossy and rust, to train the decay generator network. We show that our framework is able to synthesize diverse decay effects on various non-decayed objects without using additional decayed object images.