I'm not sure if this quite answers the question. Although Japan certainly doesn't allow bringing in content which violates their definition of pornography, it is not clear to me that these manga would fall under that definition.
The comment says, paraphrased, that rather than skimming Wiki to validate one's guess that about what the law says on the basis of one's opinion that it should logically say X or that Japan is drenched in porno so it probably says X, it is probably better to actually read the law. The text of the law is the ultimate authoritative source on whether the law covers, e.g., drawings or pictures. The law says, unambiguously, yes, it does.
The last line says, heavily paraphrased, "Some folks are probably going to think I'm saying 'lolz i can readz japanese im so cool' -- ah well".
Google translate says:
"Obscene document, drawing, or other objects to distribute, sell, publicly display, or a person who is punishable by a fine or a fine of 102 million yen or imprisonment of up to 15 years. The person who has possession of these items sell for the same."
Doesn't the US have similar statutes? (Which are almost never enforced...?)
This article skims the surface of this fairly complex topic: http://en.wikipedia.org/wiki/Pornography_in_Japan#Censorship...