One day the skies turned purple. Red doors appeared out of thin air, spouting out hideous monsters. Creatures longing for human flesh, bringing forth a deadly disease, to which scientists can't seem to find a cure to this day. Kana, a 19 year old girl is sitting inside of her apartment under her years-long lockdown, when she gazes out of the window and decides: She's had enough! She packs up and leaves the tiny room which was supposed to be her coffin and embarks on a quest to kill every monster and avenge her friend who died to the sickness. However, things don't go as smoothly as she first expected. She is quickly reminded how terrible the new world is, when she finds herself hostage in the hands of a human trafficker. That's when she meets Ash, a hunter whose job is to kill the monsters she hates so much. Their fate just seems to coincide... or... Is it really just a coincidence?