A delegation of four young Japanese envoys traveled with him back to Europe and paid a visit to several European leaders, including Pope Gregory XIII.

The expansion of Christianity in Japan continued for several decades until it was banned in the early 17th century, which remained in place until being lifted by Emperor Meiji in 1873 as part of his reforms.

The Jesuit missionary Alessandro Valignano later visited the country in 1579–82 and convinced Lord Sōrin to send Japanese diplomats to Europe, including to the Pope, on behalf of the converted daimyō.

Likewise, the four Japanese Christians were greeted upon their return in Japan by many interested in learning about Europe, and met with daimyō and imperial regent Toyotomi Hideyoshi in March 1591.

[3] It was not until 1873, during the era of westernization in Japan, that Emperor Meiji lifted the ban on Christianity, giving it religious freedom and allowing missionaries to enter the country.

Emperor Showa established relations because the Vatican had significant moral authority in Western countries, gathered information from all over the world, and he believed that it could serve as mediator between Japan and the Allies.

[6] Despite these protests, the Vatican went ahead and established full relations with Japan, accepting the diplomat Ken Harada, who formerly worked at the Japanese embassy in Vichy France, as the first country's ambassador to the Holy See.

This was satisfied by an informal agreement with Japan that the pontiff's apostolic delegate in Beijing would visit Catholic missionaries in the Wang Jingwei regime's territory.

[8] In 1944 it was reported that Harada gave Pope Pius XII indications that Japan was ready to begin peace negotiations, though later Tokyo radio denied these claims.

[9][10] In 1958 the Japanese government upgraded the legation to an embassy, also on orders of Emperor Showa, and Pope Pius XII assigned Maximilien de Furstenberg, Vatican City's delegate in Tokyo, as the first Apostolic Nuncio to Japan.