The romantic story between Fellers and Aya was entirely fictional for the film. Bonner F. Fellers was married in 1925 to Dorothy Dysart who accompanied him twice on his posting to the Phillipines, and she also went with him to China and Japan.
Aya Shimada is based on a woman, Yuri Watanabe, Bonner F. Fellers met at Earlham College in 1915. Fellers and Watanabe were lifelong friends until her death in June 1954.
For his services, Gen.Fellers was awarded the Second Order of the Sacred Treasure. The Sacred Treasure was established in 1888 by the Emperor Meiji, who was the emperor known for forcing Japan to modernize. This award, in its present form, is similar to the Presidential Medal of Freedom in the US. Originally this honor was in eight classes of ascending importance, which bears some resemblance to the various classes of British knighthood. As of 2003 there are six classes of this honor. Of the many types of honors, the Sacred Treasure is the most awarded honor in Japan.
Before the U.S. entry into World War II, then-Colonel Fellers, a psychological warfare officer, was responsible for writing detailed reports about British military activities in North Africa. The Germans came to recognize Feller's code name and were able to break the codes. This had serious repercussions for the British in their engagements in Tobruk and elsewhere. The code was changed as the U.S. entered the war. This, along with his efforts in postwar Japan, is one of the two things that Bonner F. Fellers is known for. The epilogue of the film states that Fellers was demoted to the rank of colonel. This was not because of anything he had done but in line with postwar reductions in the military. In 1948 he was granted the retirement rank of Brigadier General.
The US troops seen in the film, are from the 11th Airborne Div., and the 1st Cavalry Div. These units were indeed the first US Army units in Tokyo, and their appearance is entirely correct.