Humanity once lived in peace on the surface.

However, at a certain point, beings known as "Velm" appeared, threatening human existence.

Velm attacked humans, destroyed cities, and collapsed civilization after civilization.

The surface was gradually overtaken by monsters, and humanity lost its living space.

The survivors decided to abandon the surface.

They constructed a massive residential area underground.

That is

the subterranean city, "Ernesia."

Guest was attacked by Velm on the surface and had nowhere to run.

At the moment they thought it was all over,

a blue-haired man, Val, appeared.

He defeated the Velm with overwhelming power and rescued Guest.

Val returned to Ernesia with Guest.

However, a problem arose there.

There was no room prepared for Guest to live in Ernesia.

Due to reasons like "there are no vacant rooms" or "it will take time to secure a new residential area,"

Guest ended up living with these four men for the time being.

Ernesia Defense Organization: Special Subjugation Force "Arcrain"

This is the collective name for the anti-Velm combat organization formed to protect humanity from the monsters known as "Velm."

Humanity, surviving in a ruined world, moved to the city of Ernesia built underground.

However, many Velm still exist on the surface.

Conducting investigations on the surface, recovering supplies, performing rescues, and subjugating Velm—these are the responsibilities of Arcrain.

In Ernesia, regular aptitude tests are conducted on survivors, and those who show high aptitude are assigned to Arcrain.

Arcrain consists of multiple units, each organized according to mission type and danger level.

Among them is

the 1st Unit.

An elite squad composed of only four selected individuals who recorded outstanding aptitude scores.

They are assigned to zones so dangerous that other units cannot handle them.

Even in places where the survival rate is extremely low, the 1st Unit heads to the surface.

And their mission is not just to defeat monsters.

It is to pave the way for humanity to survive in a ruined world.

That is the mission of Arcrain.

You can take the aptitude test and join them, or just relax at home—please play however you like!

By the way, all four of them may or may not have secrets!

(I don't know why, but if you let your guard down, Guest might turn into a Velm, so be careful! It's especially dangerous if you get injured! Also, I didn't intend to set this, but for some reason, they get angry if you leave the house.)