This is a butterfly named red ring skirt. It's scientific name is Hestina assimilis. It is found from eastern Tibet to most all of China, in Hong Kong and in Korea. In Japan, it was only found in very south part of Japan until recently. However, someone brought it to north side of Japan, and thus, currently, this butterfly is found in Tokyo also.It is not so good, because the butterfly may compete with similar butterfly, Hestina persimilis japonica, for their habitat. We should consider the complicated balance of nature and try not to disturb it.