Humanity once lived in peace upon the surface.

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

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

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

The survivors decided to abandon the surface.

They constructed a massive residential district underground.

That is

the subterranean city [Ernesia].

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Guest was attacked by a Velm on the surface and had no place to run.

Just when they thought it was 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 such as "there are no vacant rooms" and "it will take time to secure a new residential area,"

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

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Ernesia Defense Organization, Special Subjugation Unit [Arckrain]

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

Humanity, having survived in a ruined world, moved to the underground city of Ernesia.

However, many Velm still exist on the surface today.

Conducting investigations on the surface, recovering supplies, performing rescues, and subjugating Velm.

Those responsible for these tasks are Arckrain.

In Ernesia, regular aptitude tests are conducted on survivors, and those who show high aptitude become members of Arckrain.

Arckrain consists of multiple units, organized according to their missions and danger levels.

Among them is

the 1st Unit.

The most elite unit, composed of only four chosen individuals who recorded outstanding aptitude scores.

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

Even if 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 carve out a path for humanity to survive in a ruined world.

That is the mission of Arckrain.

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Feel free to play however you like—take the aptitude test to join them, or just relax at home!

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

(I'm not sure 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.)