After the previous Godzilla attack, a miniature arms race ensues to collect his cells. Concerned over Godzilla's possible return, the Japanese government uses the cells to create a new bio-weapon, ANEB (Anti-Nuclear Energy Bacteria). They seeks the aid of geneticist Genshiro Shiragami, who's experiments result in a new mutation.
With the Gyaos re-emerging, Gamera's ties to humanity have been severed with his bond to Asagi broken. Nagamine and Asagi investigate while an orphaned girl named Ayana discovers a new creature she names Iris. Nagamine and Asagi must reach Ayana before she takes her revenge on Gamera, who she blames for the death of her family.
A group of seemingly ordinary merchants is really a band of assassins for hire. When they discover that all the assassins in Edo are being killed they must act quickly to find the culprit.
