Kaiju

Kaiju is a Japanese word that translates literally as "strange beast", used for the Japanese subgenre of monster films (kaiju eiga) and, in Western popular culture, as a synonym for giant movie monsters generally. The 1954 film Godzilla is credited with pioneering the subgenre, and it set the pattern: creatures of varying origins and sizes attack cities and battle the Self-Defense Forces or each other, with social and political commentary reflecting the times; Godzilla itself began as a metaphor for nuclear weapons. Rodan, Mothra, King Ghidorah and Gamera fill the classic roster, traditionally rendered through suitmation, actors in monster suits performing on miniature sets.

For novel and web-serial writers the kaiju is scale as antagonist: a walking natural disaster with a body, an origin and a symbolic payload. The Japanese giant-scale tradition it defines runs straight through mecha fiction (the rosters overlap in Mechagodzilla), and a city-destroying threat is a natural inciting engine for apocalyptic stories in the system apocalypse mold.