America actually caused Hentai.
Japan was originally a Country where nudity and walking around publically naked was 100% fine until America came along and basically told the Country to change that or die.
Japan took it too far and started censoring nudity in porn, which wasn't what America meant.
But then a Japanese guy found a loophole because the law stated shit like "All genitals are censored" And tentacles don't count as genitals, so he started using them.
And then it became mainstream.