For more details, see Part 1

A peaceful world. An ominous sound spreads through a world that seemed like it would stay peaceful forever. Then, people began to have seizures or die from the sound. Some went insane, while others were snatched by the monsters that were the source of the sound, vanishing without a trace. And this is the only photo captured of that monster.

The government named this monster פרחים. It was abnormally tall with black skin, and anyone who heard the sound it made would either go mad or die. However, those who did not go mad or die despite hearing the sound were called "Immunes." And Guest, one of those Immunes, became an official member of Team F, the unit tasked with stopping the monster. Then one day, the world began to collapse.