Tuberculosis or TB (short for tubercles bacillus) is a common and often deadly infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis in humans. Tuberculosis usually attacks the lungs but can also affect other parts of the body. It is spread through the air when people who have the disease cough, sneeze, or spit. Most infections in humans result in an asymptomatic, latent infection, and about one in ten latent infections eventually progresses to active disease which, if left untreated, kills more than 50% of its victims.
Takiko's mother, Yoshie Okuda dies of Tuberculosis before she enters the book. Takiko is shown to be immune to the disease, but in the last chapters she starts to cough blood and proves that she has the disease.