To explain why I thought this was interesting: from what I read, a Tanomoshiko is (mostly "was") an informal mechanism for loans. If one person was in financial hardship, a group of several people would each contribute a small sum of money, thus curing the hardship. Instead of ordinary repayment, the group would now repeat the same act in a few weeks, but choosing another person in the group (perhaps at random) to receive the money. This would repeat until everyone had been payed.

There were and are taboos around loans in many societies (our own included). This seems like it's probably part of a broader family of methods for working around those taboos.

I came across this only from a side remark in Yukichi Fukuzawa's autobiography. I don't know of a good source (the wikipedia article is admittedly not great).