I boost posts and advertisements for my business page all over the world - usually US, Canada, and numerous European countries, but sometimes also Japan. (If there’s any text, I translate it into Japanese with Google Translate, but it’s usually just simple pictorial graphics.) I’ve noticed on my most recent boosted post to Japan - which is boosted to specific prefectures of Japan and not just the entire country, and targeted to a certain audience (in this case, people between 20 and 40 who are interested in 90s era video game systems and baseball) that at least half, if not more, of the names of the people who liked the post, are Vietnamese sounding names, rather than Japanese characters.
This seems odd to me because I was under the impression that the population of Japan consists mostly of native Japanese. Are there really that many Vietnamese residents of Japan that numerous people in five of the different prefectures of Japan of Vietnamese origin would happen to engage with the boosted post? Or is there something about the criteria that I used that would happen to overlap demographically with people of Vietnamese origin in Japan?