US soldiers as individuals would, for the most part, not have had much direct contact with Japanese criminal organizations. Even those that participated in the incredibly normalized local and regional black markets that post-war Japan was famous for would have rarely been more involved than simply selling their American goods and foodstuffs for money, bartered goods, or services.

It should be noted that American soldier interactions with the incredibly active and lucrative black markets in Japan appeared to have been fairly common. These black markets were frequented by many common people and the supply was driven by immense, desperate demand for food, every day necessities, and of course, the rare (and expensive on the black market) luxury goods. And much of this demand was met by stolen or smuggled as well as freely traded American goods that often came from military exchanges.

Of course, policies and regulations were put into place to combat this illicit trade that supported such a burgeoning black market that readily exploited the hungry, the vulnerable, and the poor with astronomical price gouging and extortion. But the needs of so many people and the ease of access to the illegal trading combined with the large potential gain that stood to be made, even for a person casually providing goods once in a while, meant that these black markets stayed a major part of life for many Japanese people for a long time to come.

For US soldiers as a whole, or rather as an occupying authority, it's often contended that Occupation officials as well as Japanese law enforcement, complicity cooperated with various yakuza groups as well as shady far-right groups to work against far-left groups, popular labor movements, and any kind of threat to stability that could potentially give a communist revolution room to grow and mature.

Looking at the official policies of Occupation officials with the Japanese government and Japanese officials at the time points to this being an acceptable strategy for American military and political leadership at the time, considering that they were willing to completely undo reforms; actively censor media, publishing, academia, and educational institutions; as well as reintegrate many of the government leaders and officials that they initially purged when they were looking for reliable associates who had a vested interest in being extremely hard on communists and maintaining order.