Arai Hakuseki's narrative on the captivity of Pere Sidotti written in 1710 states:
"...Roxon from the time of the So and Gen until now being written Roson, jars that have come from that country are thought convenient by my countrymen to keep tea in, and the name Roson jars is understood by every one..."
The So and Gen mentioned by Hakuseki are the Sung and Yuan dynasties of China. Certainly by the early Muromachi period of Japan (1334—1467), imported tea pottery from the Namban or "Southern Barbarian" regions including Rusun was popular among the upper classes.
It could be argued though that Japan had much longer relations with the South if we conclude that the location of the Fusang Tree in Chinese tradition was found in Southeast Asia, or specifically in Rusun/Luzon. Most of the notices of travel to the location of the Fusang Tree use the kingdom of Wa, the ancient Chinese name for Japan, as a reference point, including the time of sailing from Japan to that southern region.
Also, Japanese legends of fairy lands like Yominokuni, Nenokuni and Tokoyonokuni are linked in the literature with the Chinese locations of the Fusang Tree, the Land of Yellow Springs and Penglai (Horaisan), which were generally envisioned as somewhere beyond the Southeastern Sea of Chinese texts.
This might explain why the tea jars and canisters of Rusun came to be so highly-valued aside from any practical qualities they may have possessed. It was from the earth of a sacred mountain on one of these fairy lands that the Emperor Jimmu was told to make sacred sacrifical jars during his military expeditions.
Japanese legend tells of ancient people from southern Kyushu like the Hayato or "Falcon People" who were a type of dog-man folk said to bark (inugoe) like dogs. Eventually in their role as an imperial guard caste they formally dressed like dogs and performed dog barking rituals to drive away malevolent spirits from the court, or to announce the arrival of the Emperor across provincial borders.
Another people from southern Kyushu, cousins of the Hayato, are said to have sailed to their home along the Kurushio Current. It was this "Black Tide" that brought people from the fairy lands to the Ryukyus and Japan. The Japanese might have retained knowledge of the location of this ancient region, or they just might have surmised the location later as the Kuroshio Current passes along the eastern coast of Luzon.
Rusun and Japanese Christianity
It might come as a surprise to many that Japan's "Hidden Christians" (Kakure Kirishitan) came to view Mary and Jesus as natives of Rusun, as well making Mary the wife of the King of Rusun after giving birth to Jesus!
However this is exactly what is relayed in the Tenchi no Hajimari no Koto "Beginning of Heaven and Earth," the gospel of the Kakure Kirishitan probably first printed in 1823, from earlier oral texts. The oral traditions continued even after the printed form came into being.
There have been various explanations as to why the Christian gospel would be partly localized in Rusun as well as ethnologized to the people of Rusun. The most obvious explanation to this author is the connection with the indigenous Japanese concepts of heavenly "other worlds" like Takamagahara, which they located to the south along the Kuroshio Current.
In the Tenchi, Maruya (Mary) is born in Rusun (Roson), where she eventually comes to be courted by the King of Rusun. However, as she has vowed to remain a virgin, she refuses his advances and instead ascends into Heaven. The king dies of a broken heart, and Mary is asked by God (Deusu) to return to earth so she can bear him as a child. She agrees and on one night Deusa descends in the form of a butterfly and enters the mouth of Maruya, who immediately conceives. She then undertakes a long quest to Bethlehem (Beren) where she gives birth to the child and the story connects somewhat at this time with the orthodox version.
Later, the Holy Mother Maruya asks Deusa to save the King of Rusun, which he does giving the king the title of Zejusu, and marrying Maruya and the King.
The lofty position of Maruya agrees with that of indigenous Japanese belief in Amaterasu. Maruya's ascent into Heaven could derive from the ascent of Amaterasu to Takamagahara "Plain of the High Heaven" where she bears the ancestors of the imperial family with her brother Susanoo.
Interestingly most of the Christian converts in Japan were natives of Kyushu with its traditional ties to the South. When the persecution of Japanese Christians broke out, many fled to Luzon and other parts of the Philippines where many of the missionary orders and groups in Japan were based. Those who stayed behind became the Kakure Kirishitan community of hidden Christians.
Paul Kekai Manansala
Arai, Hakuseki and W.B. Wright (translator). "The capture and captivity of Giovanni Batista Sidotti in Japan from 1709 to 1715," Transactions of the Asiatic Society of Japan, Asiatic Society of Japan, 1874, pgs. 156-72.
Hooker, Richard. Jimmu Tenno, http://www.wsu.edu/~dee/ANCJAPAN/JIMMU.HTM, 1996.
Seattle Art Museum. International Symposium on Japanese Ceramics: Transcript, Seattle Art Museum. 1973, p. 172.
Whelan, Christal. The Beginning of Heaven and Earth: the sacred book of Japan's hidden Christians, University of Hawaii Press, 1996.