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.

True adoption is not that common.

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.

Ive been pretending to be okay and acting as normal as possible, but Im actually completely heartbroken after a recent breakup. Its painful and really affecting me, to the point where I cant concentrate at work, Ive lost my appetite, I cant sleep, and It feels as if my whole world has been turned upside down. I loved him so much. He said so many cruel things to me and it made me realize he must not have loved me the way I loved him, or he wouldnt have said such horrible things. How do I handle the heartbreak and why cant I accept that he didnt love me and just forget about him?

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'.

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.

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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