A Japanese scholar has unearthed letters exchanged by Emperor Showa and Pope Pius XII that offer valuable insights into postwar relations between Japan and the Vatican.

Nihon University Professor Matsumoto Saho found the letters among documents declassified in 2020 in the Vatican Apostolic Archive. They consist of two letters from the pope and two replies from the emperor in 1952.

In a letter sent in October, the pope congratulates Japan for regaining its sovereignty and for the coming of age of the then-crown prince, who is now Emperor Emeritus Akihito. The San Francisco Peace Treaty took effect in April of that year, bringing an end to the postwar occupation of Japan.

Emperor Showa wrote in reply that the Imperial Family and the people of Japan would like to express their deep gratitude to the pope for his congratulatory message.

The Emperor is said have sought to establish ties with the Holy See two months before the attack on Pearl Harbor in December 1941 that marked the start of the Pacific War.

The annals of Emperor Showa's life quote him as saying at that time that Japan needs to fully consider how to bring an end to the war from the very start, and that it is necessary to establish amicable ties with the Vatican for that purpose.

Professor Matsumoto says it had been presumed that Emperor Showa and Pope Pius XII had personal exchanges after the war. She says the discovery of records confirming this is extremely meaningful in the study of postwar relations between Japan and the Vatican.