Shigematsu is the protagonist of Black Rain. In the present day, he attempts to prove his niece's health by returning to his diaries and describing his experience of the August 6, 1945, destruction of Hiroshima by an atomic bomb. In doing so, he embarks on a personal reckoning. Shigematsu suffers from radiation sickness due to the time he spent in the ruins of Hiroshima in the aftermath of the bombing. He still has the physical and emotional scars of the experience in the form of his changed body and the trauma he carries with him. By transcribing his diaries from the time of the attack, Shigematsu is able to wrestle with an event in his life that still holds great sway over his existence. He may claim to be working for his niece's benefit, but the secondary use of returning to his diaries is Shigematsu can gain a better understanding of the pain he has suffered. Shigematsu feels the bomb robbed him of agency in his life. Not only did Japan lose the war, Shigematsu and many others were forced to reckon with the loss of control over their own existence. The atomic bomb and the radiation sickness it caused robbed them of their ability to control their own destiny.