  We perform a systematic study of dilepton emission in a hot QCD medium based
on three different scenarios of chiral mixing, each of which yields a
characteristic structure in the vector spectral function. The in-medium
spectral functions are accommodated into the state-of-the-art hydrodynamic
simulations for a relativistic viscous fluid to calculate the dilepton
production rate, fully accounting for the space-time evolution of a created
fireball in relativistic heavy-ion collisions. We demonstrate that the
low-temperature theorem of chiral mixing extrapolated toward a chiral
crossover, often used in the literature, leads to critical shortcomings: the
inadequacy of width broadening, and a substantial overestimate of the dilepton
yield maximized around the invariant mass of $M = 1.2$ GeV. The proper
prescription offers a milder yet sizable increase in the window of $1.1 < M <
1.4$ GeV as the direct signature of chiral symmetry restoration.
