Nagai became a member of the Japan Art Academy in 1968. In 1972 he was awarded the Kikuchi Kan Prize. His 1972 novel  won the 24th Yomiuri Prize.
In 1968, Nagai was admitted to the Japan Art Academy. Two years later, he was honored with the Kikuchi Kan Prize. His 1972 literary work took top honors at the 24th Yomiuri Prize ceremony.