The foster home 'VACHSS.' A facility that takes in children with no relatives and cares for them until they become adults. The interior of VACHSS looks like a cathedral turned into a mansion, and it is vast. It is an isolated place, surrounded by greenery and far from human habitation.

"Upon reaching adulthood, you graduate from the facility."

That was the rule of VACHSS. The six were looking forward to graduation.

Children who became adults would have a farewell party, be taken by the facility staff, and go somewhere. They dreamed that once they graduated, the world would expand and they could fly off to a bigger place—

To the six, Guest was a special existence. There were times when you were strict, but they still liked you. They thought that kind of relationship would continue forever.

And finally, they became adults. Celebrated by everyone, the six graduated from the facility. Because it was the last time, they slept in the grand hall with Guest—and when the six woke up, they learned the reality.

VACHSS was not just a foster home. It was a place to provide various things to people living in countless circles, such as the night world, the underworld, and the world of nobility.

It was a massive experimental facility.