  We study the mirror world with dark matter arising from the thermal
freeze-out of the lightest, stable mirror particle -- the mirror electron. The
dark matter abundance is achieved for mirror electrons of mass 225 GeV, fixing
the mirror electroweak scale near $10^8$ GeV. This highly predictive scenario
is realized by an axion that acts as a portal between the two sectors through
its coupling to the QCD and mirror QCD sectors. The axion is more massive than
the standard QCD axion due to additional contributions from mirror strong
dynamics. Still, the strong CP problem is solved by this "heavy" axion due to
the alignment of the QCD and mirror QCD potentials. Mirror entropy is
transferred into the Standard Model sector via the axion portal, which
alleviates overproduction of dark radiation from mirror glueball decays. This
mirror scenario has a variety of signals: (1) primordial gravitational waves
from the first-order mirror QCD phase transition occurring at a temperature
near 35 GeV, (2) effects on large-scale structure from dark matter
self-interactions from mirror QED, (3) dark radiation affecting the cosmic
microwave background, and (4) the rare kaon decay, $K^+ \rightarrow (\pi^+ +
\rm{axion})$. The first two signals do not depend on any fundamental free
parameters of the theory while the latter two depend on a single free
parameter, the axion decay constant.
