Over the years, film studios have introduced monster characters who, while still considered kaiju, may be referred to by a unique title, usually either beginning with the kanji 怪 ( kai) or ending in a long 'u' in the same vein as kaijū. These kaiju adopted many classic monster traits, appearing as the 'misunderstood creature.' During the early eras of tokusatsu, 'heroic' monsters were seen in daikaiju eiga films, and it wasn't until later when television tokusatsu productions began using kaiju which aided the hero, saved civilians, or demonstrated some kind of complex personality. Others have a neutral alignment, only seeking to destroy buildings and other structures. Some kaiju are elite warriors which serve as the right-hand man to the greater villain and are destroyed by the heroic forces.

Kaiju are sometimes depicted as minions serving a greater evil. While the term kaiju is used in the West to describe monsters from tokusatsu and Japanese folklore, monsters like vampires, werewolves, Frankenstein's Monster, mummies and zombies could fall into this category (Frankenstein's Monster was once a daikaiju in the film Frankenstein vs. Chōjin Sentai Jetman features monsters based on traffic lights, faucets, and tomatoes Kamen Rider Super-1 includes a whole army of monsters based on household objects such as umbrellas and utility ladders. Kaiju are typically modeled after conventional animals, mythological creatures, and sometimes even plants though, there are more exotic examples.

Creature definition