(a) The host-subtracted optical light curves of the transient EP241021a in the r and z bands, along with the X-ray light curves during and after the plateau phase. The data were taken from X. Shu et al. (2025) and M. Busmann et al. (2025). The rebrightening, the subsequent power-law decay, and the final sharp decline are labeled in both bands. (b) The broken power-law models that fit the r-band data after a phase of 7.5 days. We present 200 randomly selected MCMC realizations for clarity. (c) The posterior distributions for each model parameter.