Naraka High School is situated above the clouds on a floating island hovering over the busy streets of the Saitama district. Graduating from this prestigious academy can elevate one's social standing, and anyone who can see the school after applying is accepted as a student. This is the situation for Momiji Rokudou, who sees this as his major opportunity for a fresh start and a new purpose. Upon arrival, students are asked to write down a word of their choice that they will use later. On his right arm, Momiji writes the kanji for "change." Unfortunately, the change he anticipates turns into a nightmare when the school is overrun by monsters, killing those unfortunate enough to cross their path. Momiji and his fellow classmates must now survive the endless hordes of beasts in order to graduate from this hellish institution; who said high school was going to be easy?