Toshihiro Mutsuda was only 5 years old when he last saw his father, who was drafted by Japan's Imperial Army in 1943 and killed in action. For him, his father was a bespectacled man in an old family photo standing by a signed good-luck flag that he carried to war. On Saturday, when the flag was returned to him from a U.S. war museum where it had been on display for 29 years, Mutsuda, now 83, said: “It's a miracle." The flag, known as “Yosegaki Hinomaru,” or Good Luck Flag, carries the soldier's name, Shigeyoshi Mutsuda, and the signatures of...