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Consensual incest between brother and sister is frowned on, but not prohibited in France. It has been legal there since the time of Napoleon, but still you can't marry your sister. It is similar in Japan, legal between consenting adults but not legal for incestuous marriages. Sweden is the only country in Europe which allows marriage between siblings who share one parent. They have recently been silently dropping anti-incest laws in other countries too. It is still technically illegal in lots of countries, but police in most countries will now turn a blind eye to it unless someone makes a complaint. Most police will leave happy couples alone these days.