This is obviously the child exploitation/trafficking group. So it seems the yakuza were actually not the ones behind it, maybe that explains the leader's harsh attitude towards Butama after he woke up from his coma? Were they genuinely surprised to find their leader involved in child abuse back then? So even though they are also exploiting Nezumi and Midori, maybe they feel as actually "taking care" of them as compensation, by giving them work and a place in the family. Pretty fucked up...