The story takes place in the near future, when monsters frequently appear in the town. Hiromi has just moved to another school because his previous school was closed. The monsters used to be dangerous creatures before, but they are now like crows or stray dogs thanks to high-quality monster exterminators. But one day, Hiromi is suddenly attacked by a monster when he meets Kiku, who has just come to the town from deep inside the mountain. Hiromi and Kiku strangely get a special power during battle and get rid of the monster. After the battle, they meet a group of girls called Shinsengumi. Hiromi and Kiku finally join the group after twists and turns. However, they conflict with another monster buster group called Kaientai, which is an official group. Also, a girl named Hiromi, who is totally the same as his deceased twin sister, appears in front of him. Moreover, they find Monster King sealed up in the basement. Like this, their three-sided fight begins now....
