@tanooki Adult adoption works differently in Asian cultures. Its primary purpose is usually not to perpetuate the family business but the family name because women can't pass on the name. Because the intent is to perpetuate the family name a marriage would be preferred over adoption in a business setting because the Japanese are surprisingly more open to female leadership in business. Japan, like China and Korea, has a system where men can marry into their wives' household instead of the other way around. They then take on the wife's family name. The husband would then be given a limited role in the business with the understanding that the wife would inherit and continue the business. Many zaibatsu still do this. This was what we readers were worried about last time. Adoption is a last resort for families who know that their daughters would marry out of the family, or have had that happen already. That's why grandma's actions are unusual.
In the context of the story Chion also has the option of becoming a female priest, a tradition Japan has had since 590CE, so there is no need for adoption just to continue the temple. Grandma just wants her to be free.