In an era in which living plants are effectively extinct, any surviving specimens seem even more beautiful due to their rarity. Those who have seen the "Shinigami Flower" have been strangely captivated and refused to let it be destroyed—even after the parasite killed a loved one by violently blooming from within their body.

Gokurakuen is Japan's national medical institution specializing in curing this infectious, carnivorous disease. Headquartered on a large ship, the hospital roams the world's seas and boasts capable doctors who respond to requests for house calls. These dedicated professionals put their lives on the line to fight the spread of the Flower, ingesting the Shinigami's poison until they start to create antibodies or die trying. However, Dr. Souma Ichinose shows greater disregard for his own life than any of his colleagues. His methods of treatment could almost be mistaken for attempted suicide, but no one—not even his assistant, Hiyo Tsubakura—knows what hidden emotions drive his behavior.