Nagao established himself among the top Asian hurdlers in the 1977 season. At the Japan Championships in Athletics that year he won the 400 m hurdles title in a time of 51.11 seconds – the best ever recorded by a Japanese athlete at the competition. He was unable to compete at the 1977 Asian Athletics Championships, as the even was cancelled due to the lack of support from the International Amateur Athletics Federation, following the exclusion of Israel from the tournament. Nagao competed at two major international events that year: he was Asia's selection for the 1977 IAAF World Cup, placing eighth, and was a bronze medallist at the 1977 Pacific Conference Games, finishing behind Australian Garry Brown and Sam Turner of the United States.