“That is how war robs you of your humanity,” he added, “by putting you in a situation where you must either kill perfect strangers or be killed by them.”

Mr. Harada said that as he and other aging veterans pass from the scene, Japan will lose more than just their war stories. He said it was his generation’s bitter experiences, and resulting aversion to war, that have kept Japan firmly on a pacifist path since 1945.

While he tries to avoid wading into politics, he let slip a jab at Japan’s current leaders, who he said seem a bit too eager to discard Japan’s renunciation of war, and too forgetful of what an accomplishment its long postwar period of peace really has been.

“These politicians were born after the war, and so they don’t understand it must be avoided at all costs,” he said. He sat on a tatami mat in his living room, which is decorated with pictures of aircraft and an aluminum fragment from the Zero in which he was shot down in 1942. “In this respect, they are like our prewar leaders.”

Similar concerns are shared by many Japanese, as the nation approaches the 70th anniversary of the war’s end. Warnings about the passing of the war generation have been voiced all the way up to Crown Prince Naruhito, 55, who in February urged his nation to “correctly pass down tragic experiences and history to the generations who have no direct knowledge of the war, at a time memories of the war are about to fade.”

Such worries have made Mr. Harada a highly sought-after public speaker. He said he has spoken dozens of times in recent years, though he has had to cut back since collapsing from exhaustion in a bathroom after a talk last year. Despite a recent diagnosis of throat cancer, he speaks with a passionate conviction that left some in the Nagano audience brushing away tears.