98% of all adoptions in Japan are of male adults so that family businesses can remain within the family.
Japanese adult adoption is the practice in Japan of legally and socially accepting a nonconsanguineous adult into an offspring role of a family. The centuries-old practice was developed as a mechanism for families to extend their family name, estate, and ancestry without an unwieldy reliance on bloodlines. Adult adoption is still common today as a dynamic tool for social and economic mobility.
There is evidence that this practice began as early as sometime in the 13th century within the sect of Buddhism known as Pure Land Buddhism but only really became widely used in the Tokugawa (or Edo) period, which began around 1600 and lasted until 1868.
During the Tokugawa period, much of the Samurai class would adopt sons to create a strong, fixed position in society by assuming positions such as the head of household and the head of the business. It was also a way for households lacking sons to continue a patrilineal line and remain a functioning societal power; this was its most common purpose but was also seen by the adoptees to climb the social ladder by leaving the title of the second son, etc. behind.