The series provides few details about her life before its start. She is an adopted child, with her birthplace unknown to the reader, although she claims she's from an island "to the left." Koiwai, Yotsuba's adopted father, says he met her as an orphan in a foreign country and before he knew it he was raising her as his own; she is sometimes taken for a foreigner by strangers. When asked about her mother, she doesn't understand the question, and she gets confused by the concept of having two sets of grandparents. Before moving to her current home, Yotsuba lived in the country with Koiwai and his mother. She initially claims she is six years old, but her father later corrects this, saying she is in fact five years old.