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.
Nagai became a part of the Japan Art Academy in 1968. By 1972, he had earned the prestigious Kikuchi Kan Prize. That same year, his novel secured first place at the 24th Yomiuri Literary Competition.