Simulated X-IFU spectrum for varying Milky Way hydrogen column densities with O VII and O VIII absorption features at z_WHIM = 0.3. Input lines have equivalent widths of EW_O VII = 0.28 eV and EW_O VIII = 0.19 eV. Afterglow spectra have a starting flux of F_start = 5 × 10⁻¹¹ erg cm⁻² s⁻¹. Top: hydrogen column density of 10²⁰ cm⁻². Middle: hydrogen column density of 10²¹ cm⁻². Bottom: hydrogen column density of 10²² cm⁻².