A mysterious organization called Salvacion has deemed humanity to be a blight on the Earth, and nigh-indestructible bio-monsters called "Kan" roam the Earth under its control, literally absorbing any humans they come in contact with. Humanity's only hope is a young girl named Arina, a genetically-engineered bioweapon immune to the Kan's absorption and possessing incredible power. However, Arina still has the mind of a child -- she's naïve, impulsive, and entirely shameless. Arina, along with her adoptive father Akira Satomura, travel Japan doing their best to stop Salvacion and the Kan from destroying humanity.