This sect of Buddhism, called Jodo Shinshu, is associated with the Honganji temples located near Kyoto.
Sons associated with the Honganji would be adopted out into prominent families of the surrounding areas.
Still common today, adult adoption is a dynamic tool for social and economic mobility.
During the Tokugawa period, much of the Samurai class would adopt sons for the purpose of creating a strong, fixed position in society through the assumption of positions such as the head of household and the head of the business.
From the point of view of the adopted son, it was not so much an increase of class position, but rather a way to receive an independent life by becoming a first-born son.
This does not mean that there were no vertical jumps in the social stratum by less wealthy individuals, but it was significantly less common.
The centuries-old practice was developed as a mechanism for families to extend their family name, estate and ancestry without an unwieldy reliance on blood lines.In the early 20th century for example, becoming a mukoyōshi was considered an embarrassment or even emasculating.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.It was a way for families to ensure the continuity of a reliable male line that would take over as the family head and sometimes the head of the family business.Adult adoption lost some of its steam during the following years after its use in the 13th century.By being adopted, second-born sons were able to take over as the heads of households, and become the leader of the family business as well as a leader within the community itself.