Kaiju is a term used to refer to a giant monsters which might replace Mutations since not all monster are mutants, as most of extraterrestrial aliens, guardian entities, and ancient creature.

Another there is like there are two Godzilla, each monsters come in two which mostly the adult monster and it young which are mostly an egg.

The adult monsters were either mutated or awaken since 1960s as the same time as the original Godzilla then later resurface in the late 1990s.

Most of the first generation monsters are violent, aggressive, and territorial to Godzilla but their next generation are more friendly toward him.