Japanese culture: Is it true adult adoption is common in Japan?

This is due to the fact that Japanese civil law prior to WW2 did not allow one to choose to adopt a woman's surname when they married. If he really wanted to choose a woman's surname, he had to be adopted into a woman's family and married at the same time.

There are two main current examples of this being done: firstly, because a family with a very large estate but no heirs wants to create a new person to manage the estate. The other is for gay people who want to marry in Japan, where same-sex marriage is currently not possible, to be legally recognised as a family. Neither is very common, considering the overall percentage of the population.

True adoption is not that common.

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This derives from the way surnames are decided when getting married in Japan. In Japan, when people legally marry, they are required to unify their surnames to one of them: around 90% of people unify their surname as a couple using the male surname, while the rest adopt the female surname. This unification with the female surname when getting married is a kind of slang for 'adopted'.

This custom died out after WW2, but the word 'adopted' remained in the language. It has actually been used as the title of a manga.

However, if you read the Japanese literature with automatic translation, you will find many more references to "adopted"(養子) than this.

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