Sex in Japan is a knotty issue — even if you're not a fan of tying up your lover with rope, also known as shibari. No matter how you write about it, it raises ire. If you point out that Japan has a vibrant sex industry in which every sexual act other than vaginal penetration can be legally bought and advertised, you're accused of promoting prostitution.
Incidentally, prostitution in Japan is de facto defined as a woman selling herself to a man — gigolos are free to sell themselves. Sexual discrimination at work again. And while prostitution is illegal, neither the customer or the prostitute are punished — only the pimp, brothel or facilitator.
But my point is that talking about sex in Japan is a troublesome thing. Ask Osaka Mayor Toru Hashimoto (see Dark Sides passim).