It's against German law to publish and buy NSFW games on Steam. In Germany there are no NSFW games on steam.
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Well the publisher can publish the game on steam but only for every other country. In germany the problem is just that steam has no age verification, so all NSFW games are cancelled by steam for the region. That´s just because steam don´t want to put the verification system in, so all NSFW games on steam are aviable all over the world but not in germany...