  We study the hybrid inflation with a pseudo-Nambu-Goldstone boson inflaton
and two waterfall scalar fields. The $Z_2$ symmetry for the waterfall fields
keeps inflaton potential flat against quantum corrections coming from the
waterfall couplings, and it is broken spontaneously in the vacuum without a
domain wall problem within the Hubble horizon of our universe. We show that the
$Z_2$ invariant Higgs portal couplings to the waterfall fields are responsible
for the reheating process, leading to a sufficiently large reheating
temperature after inflation. In the presence of an extra $Z'_2$ symmetry, one
of the waterfall fields or another singlet scalar field becomes a dark matter
candidate. In particular, we find that preheating is sufficient to account for
the correct relic density of the waterfall dark matter.
