  We investigate the cosmology of mini Primordial Black Holes (PBHs) produced
by large density perturbations that collapse during a stiff fluid domination
phase. Such a phase can be realized by a runaway-inflaton model that crosses an
inflection point or a sharp feature at the last stage of inflation. Mini PBHs
evaporate promptly and reheat the early universe. In addition, we examine two
notable implications of this scenario: the possible presence of PBH evaporation
remnants in galaxies and a non-zero residual potential energy density for the
runaway inflaton that might play the role of the dark energy. We specify the
parameter space that this scenario can be realized and we find that a transit
PBH domination phase is necessary due to gravitational wave (GW) constraints. A
distinct prediction of the scenario is a compound GW signal that might be
probed by current and future experiments. We also demonstrate our results
employing an explicit inflation model.
