  Scalar field with generalized kinetic interactions metamorphoses depending on
its field value, ranging from cosmological constant to stiff matter. We show
that such a scalar field can give rise to temporal enhancement of the curvature
perturbation in the primordial Universe, leading to efficient production of
primordial black holes while the enhancement persists. If the inflation energy
scale is high, those mini-black holes evaporate by the Hawking radiation much
before Big Bang nucleosynthesis and the effective reheating of the Universe is
achieved by the black hole evaporation. Dominance of PBHs and the reheating by
their evaporation modify the expansion history of the primordial Universe. This
results in a characteristic feature of the spectrum of primordial tensor modes
in the DECIGO frequency band, opening an interesting possibility of testing PBH
reheating scenario by measuring the primordial tensor modes. If the inflation
energy scale is low, the PBH mass can be much larger than the solar mass. In
this case, PBH is an interesting candidate for seeds for supermassive black
holes residing in present galaxies.
