Keiko is a female infant with black hair, the baby sister of Ichirou (also known as Itchan), and a member of his family unit. She shares a mother with Ichirou. Her existence unfolds within Itchan's household during the final days of World War II in a smaller Japanese city, a setting marked by food scarcity and the constant threat of air raids. As an infant in this wartime environment, no specific actions, dialogue, or narrative function beyond her familial relationship are detailed.