Who took Roman glass to Japan?

Multilayered beads of Roman glass had been found in a 5th century tomb in the Japanese town of Nagoka near Kyoto in 2012 (1 and 2). Now it has been confirmed that a dish and a bowl found in another 5th century grave located near Kashihara, Nara Prefecture, are also of Roman making.

"The dish and bowl were retrieved together from the No. 126 tumulus of the Niizawa Senzuka cluster of ancient graves, a national historic site. The No. 126 tumulus dates back to the late fifth century. According to the team’s analysis, the chemical composition of the clear dark blue dish is almost identical to glasswork unearthed in the area of the Roman Empire ... Measuring 14.1 to 14.5 centimeters in diameter, the flat, raised dish is believed to have been created in the second century at the latest. ...

(Provided by the Tokyo National Museum)3

The scientists used a special fluorescence X-ray device to analyze chemical elements in glass powder from the dish. The chemical compositions of natron, a type of sodium mineral, as well as sand made of silica and lime, resemble those typically found in Mediterranean glasswork produced in the Roman Empire and the following Eastern Roman Empire period. The team also conducted a fluorescence X-ray test on the dish using a high-energy radiation beam at the Spring 8 large synchrotron radiation facility in Sayo, Hyogo Prefecture. The test revealed antimony, a metallic element believed to be used in Rome until the second century.

The results mean that it took centuries for the dish to arrive in Japan and be buried in the grave after it was produced in Rome.

Abe and his colleagues also revealed that the chemical composition of the cut glass bowl is the same as that of glass fragments unearthed from the remains of a palace in the ancient Persian capital of Ctesiphon." (3)

Note that the beads found in Nagoka also contained natron, which supports the evidence that they originated in the Roman Empire. (2)

Mentioning Ctesiphon as the likely source of origin seems to place a delimiter to the time when the bowl may have been made. There were very few periods when the capital of Parthia (not Persia) was occupied by Romans; one of them was 164 A.D. when legatus Avidius Cassius had captured it during the war against king Vologaeses. Incidentally, about that time a self-styled embassy of emperor "An-Tun" (probably Marcus Aurelius Antoninus) popped up at the Chinese court, according to a Chinese source named the Hou Hanshu. Is it possible that beads, bowl and dish were all brought to Eastern Asia by this very trading convoy and sold or presented much later to Japanese noblemen? 

In "Opus Gemini", the second trilogy of the "Romanike" series, Avidius Cassius' campaign against Parthia is supported by his distant relative, princess Iulia Balbilla of Commagene. Several characters of the series are members of the trading convoy to China. Perhaps the bowl and dish should be mentioned in a future revision of our books?