Kaiju (怪獣 kaijū) is a Japanese word that means “strange creature,” but often translated in English as “monster” or “giant monster”. It is used to refer to the kaiju genre of tokusatsu entertainment.

Daikaiju, the Dai prefix implies a larger size, in universe these are anything larger than Colossal.

Kaiju exist in this universe, drawing inspiration from the old movies like Godzilla as well as the more recent visit to the genre like Cloverfield and Pacific Rim.

Each Kaiju is unique and different, if they take serious damage they’ll naturally retreat and return with evolved means to deal with what damaged them the most. Where they come from is unknown but the large sea the nations surround seems to hold their breeding ground, or at least the most common place for their nests.

Kaiju Status in Universe

Kana’s Kaiju (Kaiju): Unknown, Escaped the battle for the First Flame.
Ripple-Hide (Daikaiju): Killed, body infested with Annelids.