Nanami Ishikawa (Takako Tokiwa) works as an editor at a publishing company. She travels Hiroshima to go after her father Asahi who left home. During her visit to Hiroshima, she learns about the tragic story of Asahi's older sister Minami Hirano (Rina Kawaei). When Minami Hirano was 13 years old, she was exposed to radiation by an atomic bomb.