I did a bit of fact finding on the Net and this is what I found. I have written in my own words and sharing with you all.
You would have also wondered, why Japanese porn shows breasts clearly. Aren’t breasts also a part of nudism and porn? Much of Japanese porn originates from its paintings, known as shunga. There was not much difference visible between the chests of both men and women who appear in the paintings.
Unlike present beauty standards which value big breasts, preserved shunga prints show that the Japanese never really eroticised boobs and, although this was dependent on class, it was not uncommon for Japanese women to be topless.
In 2004, for the first time, Article 175 was used against Suwa Yuuji, creator of the manga Missitsu or Honey Room. Yuuji was convicted for distributing "indecent and explicit" material through his artwork. He was fined equivalent of INR 2,87,829 and avoided imprisonment after pleading guilty to the charges levied against him.
But the artist took his case to the highest court in Japan, arguing that Missitsu was not nearly as graphic in its depiction as a lot of other material that was freely accessible on the internet.
However, the Supreme Court of Japan held that Yuuji was in the wrong and tripled his fine to equivalent of INR 8,63,420.
Though we see lots of Japanese porn, 46% of Japanese women and 25% of Japanese men between 16-24 abhor the idea of sex. 40 per cent of Japan's millennials and almost a third of those entering their 30s are virgins.