The story follows Kakujō Yōkō, his fifteenth birthday in a seemingly normal world where medical technology has sky rocketed and is now able to transplant any human organ. Those behind this are called the Ame No Tori (Rain of Birds). But it all turns out to be a plot against humanity where the new tech can take over its host and thus making them into a killing machine. A task force called the Jackalope are set on annihilating them before they raise more havoc and so Yōkō's new life begins.