Known as a Rogue Hero in the fantasy world Arezard, Akatsuki decided to take upon the request of the defeated Demon King to take his daughter with him. After bringing her back to the world he came from, Akatsuki brought her to join Babel, an academy-like organization that specializes in training those who came from the other world.
In the near future, Tokyo was left flattened as a result from a great earthquake. A new city, MegaTokyo, was then recreated due in no small part from the aid of a multi-million dollar company, Genom Corp. Genom created and mass-produced biomechanical creatures called Boomers to aid in the restoration of MegaTokyo. When the Boomers began to run out of control, the ADPolice at first tried to stop them, but they proved to be far more difficult to deal with than was first imagined. Under the ever looming Boomer threat, a group of four girls from varying degrees of society banded together. Calling themselves The Knight Sabers, they were the only ones with enough firepower and resourcefullness to defend the fledgling MegaTokyo from Genom and its berserk Boomers.
Naota is a normal Japanese 6th grade boy (although a little cynical), but when his older brother leaves for America to play baseball, his brother leaves his 17 year old girlfriend Mamimi behind. Mamimi is sending mixed signals and advances to Naota, and he doesn't know what to do about her. But to make matters worse, Naota's world is totally turned upside down when he is run over by a woman on a Vespa. During their first encounter, she hits him over the head with her guitar, which then causes a horn to grow out of his forehead. She calls herself "Haruko" and her presence changes Naota's life to even further insanity.
In their closed-off underground village, Kamina and Simon chafe at the limits imposed by the village elder. Yet all this will change, when Simon stumbles across a fantastic device—just as the village's peace is broken by a violent intrusion.
Takashi Komuro is a normal high school boy, until an infection breaks out that turns people into zombie-like creatures. Along with his friends & the school nurse, they fight their way out and continue their journey to find out what exactly has happened to the world.