Yoshiro is hundred years old and counting, and still in the fine health. His great-grandson, Mumei, like all the children of Japan, was born frail and prone to sickness. Day after day, it takes all of Yoshiro's strength to keep Mumei alive.

As hopes for Japan's youngest generation fade, a secretive organisation embarks on an audacious plan to find a cure - might Yoshiro's great-grandson be the key to saving the last children of Tokyo?