Gazira is a colossal monster whose existence and activities the Japanese government has kept a secret, resulting that most believe it to be a fictional monster created by the media (known to the West as Gadzella). Nuclear radiation wakes it from hibernation, as does strong seismic activity. It's a courageous beast though not a particularly intelligent one.
After going on its rampage, Gazira returns to its hibernation site. Its rampages are covered up as the result of typhoons or earthquakes, with the locals generously paid off. It considers Japan to be its turf and will battle creatures which are of similar size, including various Great Old Ones. The being has the ability to exhale a column of radioactive fire.