  We consider a light dark matter candidate which is produced by the freeze-out
mechanism with $3\rightarrow2$ annihilations, the so called Strongly
Interacting Massive Particles (SIMPs). SIMPs are identified as dark pions in
dark chiral perturbation theory (ChPT) where both light mass and strong
coupling needed for SIMPs can be realized by strong dynamics. In QCD-like
theories with $SU(3)_L \times SU(3)_R /SU(3)_V$ flavor symmetry, including dark
vector mesons in the hidden local symmetry scheme, we illustrate that dark
vector mesons unitarize the dark ChPT efficiently, thus determine the correct
relic density condition within the validity of the dark ChPT.
