Kaiju, are very strong, very big Yokai, who live in the sea. Unlike most Yokai, they rarely interact with the outside world.
Almost all Kaiju are absolutely gigantic in size, a "small" one towering at seven-stories tall. They have a monstrous visage about them, with features normally similar of an aquatic dweller. Though they all fall into the same species, Kaiju came in many different forms and designs, with all kinds of appearances.
Kaiju normally dwell at the bottom of the ocean, in deep crevices and trenches. They prefer solitude and privacy, favoring isolation from the world above them. Some Kaiju will occasionally venture onto land if they see fit, for interaction with other Yokai.
The majority of Kaiju are relatively unintelligent, having a philosophy of hit first, ask questions later. They are poor strategists and tacticians, generally just trying to force their victory. For this reason, they are seldom taken seriously by other Yokai, and considered to be weak for their low intelligence. There are, however, a select few Kaiju who display remarkable intelligence and cunning, and are capable of forming strategies and plans.
All Kaiju have a strict sense of camaraderie towards one another and will almost always team up with other Kaiju to defeat their enemies. They have a strong feeling of devotion and duty towards their brethren, and if a Kaiju calls for help, another Kaiju will often answer it.
Despite their violent, and tremendous appearance, they still do have human-forms, though they rarely have a reason to enter them.
A Kaijus most obvious advantage, is their colossal size. In terms of brute power and strength, they can be considered to be the mightiest of all the Yokai, though their low intelligence will often inhibit them.
Most, but not all, Kaiju are capable of breathing fire, and can sometimes manipulate the fire to their own ends. Some are capable of roaring with such force, that it creates an enormous wave it is capable of bringing down entire buildings with just a single roar.
All Kaiju are very good swimmers, and are capable of breathing underwater. They are still capable of breathing on land if necessary.
Kaiju are strange, in the fact that they have three lungs. They have two primary lungs which they use to breath normally, but their third lung is different. Within it, oxygen is concentrated, and mixed with a series of different gases that are produced naturally in the organ. As a result, the gas is highly flammable. When they need to use their fire breath, they will open up a pipe that leads to their third lung, and exhale strongly. The result of the gas from the lungs, hitting the oxygen in the air, and the carbon dioxide being exhaled from the primary lungs, results in a huge stream of fire.