  The hot, neutron-rich, and dense circumstance in core-collapse supernovae
provides a source of negatively charged pions that may make up a significant
portion of the matter. These abundant thermal pions can play a role to populate
light and hidden hypothetical particles. We discuss the dark gauge boson
production via reactions involving supernova pions, the rate of which is
determined by the isovector nucleon coupling. We take into account the two toy
models, the dark photon and the gauged $B-L$ models, that carry the typical
distinct isovector nucleon coupling structure in the medium. Pion-induced dark
gauge bosons leave an imprint on several observational consequences associated
with supernova. Their sizable emissivity and characteristic hard spectral
distribution result in the stringent constraints on the dark gauge boson
models, in particular at masses above the two electron mass.
