Yukio Seki was born 1921 in Iyo Saijō, a small town in Shikoku. His parents ran an antiques store specializing in tea ceremony utensils. At an early age, Seki was exposed to Naval training courses at his middle school and planned a career in the Navy. Since naval personnel were fully prepared to die in battle, and since Yukio was an only child, the family adopted a daughter nearly Yukio's age to carry on the family affairs.