We present a comprehensive spectral study of the supersoft X-ray source RX J0925.7-4758 using six observations from ASCA, Chandra, XMM-Newton and NICER, spanning 25 years. Our primary objective is to identify a robust non-local thermodynamic equilibrium (NLTE) spectral model that consistently fits the continuum emission across all data sets. A systematic fitting procedure revealed that only a pure-hydrogen NLTE model with effective gravity \(\log g = 7\) could achieve acceptable fits for all observations. The composite model incorporates photoelectric absorption, interstellar medium (ISM) absorption with non-solar abundances and discrete absorption edges at known threshold energies. The effective temperatures are found to be of the order of \(\sim \!\!\! 10^{5}\) K and the luminosities are estimated to be \(\sim \!\! 10^{41} \mathrm {erg\, s}^{-1}\) , suggesting that the emission arises from a hot accretion disk around a white dwarf undergoing steady hydrogen burning. Additionally, we examine the relative strengths of the bound-free absorption edges in all six observations. While consistent trends are seen in earlier missions, the NICER data show variability in edge dominance, likely due to the instrumental or calibration differences. Although the continuum spectra can be modelled satisfactorily, high-resolution grating spectra from XMM-Newton reveal complex line features, including P Cygni profiles, which are not reproduced by static atmosphere models. This highlights the need for future NLTE+wind models to interpret these data more completely. Our study lays a foundation for such future analyses of high-resolution grating spectra of supersoft X-ray sources.
