Ikuru Yoshizumi has spent the last decade of his life suffering from a terminal illness, and his death quickly approaches. Seeking a reason to carry on in his final days, Ikuru applies for ownership of an AGH-RMS, a genetically engineered human with a short lifespan, designed to provide comfort for those who are on their last legs.

Ikuru is given Ai, an AGH-RMS who appears and functions as a girl his age. Ikuru finds his own reason for living within Ai, who is able to develop her own personality through her pure love for Ikuru. As unpreventable global conflict threatens the future of the human race, Ai and Ikuru cling to each other for safety and understanding.