Shukugawa Meguri is afflicted with an illness called the “Oumon” disease. At this point in time, nobody knows its cause, and there’s no real treatment for it yet. The only option with a slight chance of success, is to undergo a heart transplant. But finding a compatible heart is something that can be compared with a miracle. For that purpose Meguri’s sister, Ria, was actually born as a designer baby. So that her heart could be used “like a spare”.

This is the story about two sisters, the youngest born for the sake of the eldest. Other than their family, only Meguri's best friend Ryuuji knows about their secret. Her resolve wavers during the little time they have left. What will be the conclusion at the end of these emotional moments?