Yasui was born in
Hikone,
Shiga. He carried on his father's name, Kizo. The last Kizo Yasui, father of this Kizo Yasui, was nicknamed
Kōshō Chōchō［Commercial College Town Mayor］because he was elected Town Mayor of
Hikone Town against his will while he was in Tokyo to negotiate the establishment of
Hikone Commercial College（now, the Faculty of Economics of
Shiga University）and resigned his post of the Town Mayor of
Hikone when he saw new-facility construction of Hikone Commercial College. His older sister, Kinu, married into a distinguished family in
Akasaka-juku (Nakasendō), the Yabashis that
Emperor Shōwa officially visited in 1946.
Otohiko Hara (
jp), formerly Otohiko Yabashi, is his nephew.
Shinya Yabashi and
Hideroku Hara (
jp) are his grandnephews. Yasui graduated from Shiga First Junior High School (now, Shiga Prefectural Hikone Higashi High School) and from Tokyo College of Commerce (now,
Hitotsubashi University) in 1926 under the old system of education. While in the College, he joined the seminar of Prof. Kin-no-suke Otsuka. He entered
Mitsui Bank after graduation. He became managing director, senior managing director and vice-president of
Mitsui Bank in 1959, president of Mitsui Petrochemicals Industries (now,
Mitsui Chemicals) in 1961,（
jp）, former Vice Minister of Ministry of Finance and former president of
Japanese National Railways. == Kinship ==