For the yakuza it doesn´t matter were you comes from, which country or from which class of society you belongs to, you can become a member anyway. Yakuza takes care of the misfits in the society. Yakuza members can be youth that been abandoned by their parents, youths that not managed the high pressure from the school, refugees from Korea, China etc.
Their nearest boss becomes like their father and their comrades as brothers. Yakuza offers not just companionship also money, status, authority. A part of a group were you feel useful and needed. Comparing with gangs in the USA suburbs.
There is no thresholds or requirements in order to become a member. But when you are inside there are obedience to the superiors.