Каме может, и я смогу
To foster this kind of blind loyalty, it was necessary for the yakuza to implement a system of reliance. This resulted in the oyabon-kobun relationship (roughly father role - child role), popular among the bakuto already during the seventeenth century. In such a relationship, the oyabun "adopts" kobun, offering them protection, advice and work in exchange for servitude. This may sound strange to a westerner, but in Japan such family loyalty is natural; a father is simply meant to be obeyed.
The adoption ceremony is known as sakazuki-goto (sakazuki being a small sake cup), and consists of the participants taking turns drinking from the same cup in what is originally a Shinto ritual. The kobun keeps the cup after the ceremony, both as a memento and a physical contract - it has to be returned or destroyed in case of an expulsion. The kobun may later hold sakazuki-goto ceremonies of his own and thus adopt kobun of his own. Through this method the family will grow and branch off, to the point where a new family may be formed.
lparchive.org/Yakuza/Info/
The adoption ceremony is known as sakazuki-goto (sakazuki being a small sake cup), and consists of the participants taking turns drinking from the same cup in what is originally a Shinto ritual. The kobun keeps the cup after the ceremony, both as a memento and a physical contract - it has to be returned or destroyed in case of an expulsion. The kobun may later hold sakazuki-goto ceremonies of his own and thus adopt kobun of his own. Through this method the family will grow and branch off, to the point where a new family may be formed.
lparchive.org/Yakuza/Info/