Still common today, adult adoption is a dynamic tool for social and economic mobility.
It also was a way for households lacking in 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 as a way to climb the social ladder by leaving the title of second son, etc.
This sect of Buddhism, called Jodo Shinshu, is associated with the Honganji temples located near Kyoto.
When families would find themselves lacking either a capable male heir or a son altogether, they would turn to adoption by marrying a man to one of their daughters, or just merely taking them into their household.
Adopted sons (during the Tokugawa period, especially in the early years) usually were a part of the same social circle and income level.
[1] The popularity of this practice rose steadily throughout the Tokugawa period, and soon became a common occurrence among social groups other than Samurai.
It is also worth noting that to think of succession as tied through the possession of an heir and that lacking one is the only historical cause for adoption is reductive, even in generality; complexities such as "passing over" a firstborn and adoption while already having an heir have strong historical precedent throughout the Tokugawa era.
In the absence of a gain of power or capital, a mukoyōshi could be equated with a bride as he adopted a new surname and adjusted to his in-laws.
One of the most popular was created by Chieko Date and enables families to meet with potential suitors for their daughters.
[11] Japan is characterized by a bilateral kinship system including patrilineal and matrilineal elements of descent recognition.
Adult adoption, just one solution to the restrictions presented by a rigid system of succession, ensures the presence of a household head.
[12] Adoption secures a full legal, ideological, and kinship role as a son or daughter for an adoptee.
Adopted adults also accept the responsibility of the adequate care of the family's ancestors in accordance with Buddhist doctrine.
[16] If the adopted male heir falls short of success, he can be passed over and disinherited from the family, although it is very rare.