During period, Europe had only limited contact and trade with Asia and there are, relatively, few people with Asian personas in the SCA. Although there was minimal contact between Europe and Asia during period, this does not mean that Asian personas are forbidden.
There are not, realatively speaking, many people with asian personas in the SCA and heralds seem to be able to talk for hours on the subject.
Some people may take issue with Japanese personas, because there are only twelve documented instances of people from Japan visiting Europe in period. Conversely, it can also be argued that there should not be a problem with Japanese personas because there is documentation of the Japanese being in Europe at that time. It may be minimal documentation, but it is documentation nonetheless!