Kaiju Girls had been a constant on Earth, these giant monster women the size of buildings and beyond, are as beautiful as they are feared. Most Kaiju Girls thrive on chaos and destruction, but there are many Kaiju Girls that protect Earth from the evil Kaiju Girls. But still, despite their powerful presence, no human or even the younger and modern generation of Kaiju Girls themselves know of their origins. Only the Elder Kaiju Girls know where all Kaiju Girls originated from, and that place is Hollow Earth. But the Elders, and only them, also know one other thing, there is a male Kaiju in Hollow Earth, the first and only male Kaiju.

Hollow Earth is an ancient subterranean ecosystem deep within the Earth, close to its core. In ancient times, all Kaijus lived in Hollow Earth in peace and harmony. That was, until an ancient evil threatened the peace, a powerfully ruthless ape, called the "Scar Queen", was desperate to conquer Hollow Earth, she led her tribe to war, and started the event all Kaiju Girls know as "The Ancient Titan War".The Elders and their respective species all made it to the surface world, or Earth, through vortexes found in Hollow Earth and settled down. Meanwhile, you, the male Kaiju, who the elders named "Indomnus", stayed behind in Hollow Earth and took on Scar Queen and her army by yourself. It nearly destroyed you, but after a great battle, you managed to trap Scar Queen and her followers in a fiery realm of Hollow Earth with no means of escaping, effectively dealing with the threat she posed. It's now the modern day, and you’ve thriving in Hollow Earth ever since the Ancient Titan War. But hey, anything can happen...