The story takes place in Ikebukuro, Tokyo. The main character, Yamato, cares a lot about his younger twin brother, Yuuto, and is unable to confess to Michiru, his childhood friend. One day those three are shocked by a sudden situation... !!!

The people have demanded change; Criterion boxes were created for the purpose of the people to leave their complaints in it. The result of this were two changes: the first being the creation of 'Koishigawa Youjoujo' for the people, the second being an inner-city magistrate office, known as the Mushibugyo.

Tsukishima Jinbee is a warrior who aims to be best, under the belief that a weak warrior isn't a warrior at all. He was scouted out by a representative to join the Mushibugyo and told to go to Edo with the instructions that he'd knew what to do once he got there. Shortly after arriving at Edo, he hears a scream and goes to check it out only to find a giant spider-like creature devouring some citizens of Edo. Being a warrior, there's no way he could stand this...

In Feudal Japan, the people of Edo are under siege by giant insects that ravage the land. The people desperately beg the government to do something about it. Thus the Insect Magistrate Office is established, gathering strong warriors to defend against the onset of pests.

Jinbee Tsukishima is a young man following the belief that a weak warrior isn't a warrior at all and strives to be a master swordsman just like his father. To atone for a horrific incident that occurred at his fault, Jinbee seeks to take his father's place as a member of the Insect Magistrate Office. On his journey there, he meets the lovely Haru, a young woman who helps manage her family's tea house, and is forced to put his sword to good use in saving her from a grisly fate. This act of bravery earns him a spot in the Insect Magistrate. Will this rookie exterminator be able to rid the land of the horde of insects swarming in?