The near detector of the T2K experiment has recently undergone a major upgrade. New Time Projection Chambers have been constructed, based on the innovative resistive Micromegas technology. A resistive layer is deposited onto the segmented anode in order to spread the charge onto several adjacent pads. This way, the spatial resolution for a given segmentation is improved. The results of the first detailed characterization of the charge spreading in resistive Micromegas detectors will be presented. A detailed physical model has been developed to describe the charge dispersion phenomena in the resistive Micromegas anode. The detailed physical description includes initial ionization, diffusion effects and the readout electronics response, including description and simulation of noise. The model provides an excellent characterization of the charge spreading of the experimental measurements and allowed the simultaneous extraction of gain and $RC$ information of the modules.