The panic caused by "UNKnown-LV4" in 199X plunged Japan into the depths of fear twice. However, even that terror has now become a thing of the past.

Amidst the devastation of that panic, some boys and girls lost their families. They were raised in a certain facility, like real siblings.

But the facility - their only home - closed down, and they went their separate ways, making a promise to meet again in this place.

Time passed, and they reunite at the promised spot. Along with an uninvited darkness.

[Translated from the official site]