I have a feeling that I'm most qualified to speak about this, being a mother of two grown kids...
Circumcision is not common practice in Japan. Reports say that 60% of Japanese men are not circumcised. The medical technology is there, but Japanese doctors and obstetricians do not believe it is necessary unless it is a serious health impediment for the person. There are foreign-trained doctors who urge it is necessary for sanitation, etc., but the general population remains unconvinced, because serious medical cases have not developed (in significant numbers) from non-circumcision.
When my son was born (twenty-some years ago), the doctor didn't even ask me if I wanted him circumcised. Not doing it was a given. As far as I know, he doesn't have any problems because of this.
When my brother was born, however, my mother gave birth with a US-trained doctor and was advised that the baby should be circumcised. The times were that most Japanese blindly believed everything American is good, so she agreed, convinced that it was state-of-art medicine. So, he's one of the small number of Japanese men who have been circumcised. My mother and my brother tell me now that it was probably not necessary.
FYI, that type of surgery is called 窶「テッナ痴ナスティツ術ツ(窶堙吮?堋、窶堋ッ窶堋「窶堋オ窶堙」窶堋カ窶堙」窶堙つ)
Circumcision as ritual is called ナ?窶樞?氾ァツ(窶堋ゥ窶堙や?堙ェ窶堋「ツ)
HTH!