Kaijus (Japanese: 怪獣 kaijū, strange beast) are a race of amphibious creatures genetically engineered by the Precursors, a sentient race from the Anteverse.
In 2013, the Precursors opened a portal once again, between dimensions at the bottom of the Pacific Ocean, allowing the kaijus to enter Earth's dimension for the second time since the Golden Samurai defeated the kaijus. As biological weapons of warfare, most kaijus are extremely hostile and toxic creatures designed with the intention to wipe out all all kinds of sapient species, while Godzilla and his allies aren't extremely hostile, but they are still peaceful, and had intentions to protect all sapient species from the evil kaijus, and help the Jaeger pilots overthrow the Anteverse, and capture the kaijus for them.
Today, then can be best pets used for Jaeger pilots, retired or still active.