This final installment of the recent Gamera trilogy begins with schoolgirl Ayana discovering a large egg in a cave that, according to legend, houses demons. The egg hatches into a small monster, which Ayana decides to raise and quickly develops a psychic bond with. As Ayana's monster, named Iris, grows to adulthood, the flying turtle Gamera begins to take an interest in this new potential threat. Who will be the victor in the final battle, and how much of Japan will be left standing at the end?
