The Moriyama family is an immigrated yakuza group from Japan. Kengo Moriyama brought the family to the US a couple of decades ago. Their business is described as normal by the media and is only under scrutiny by the press due to high profile of Edgar Allan's Ravens. Riko's estrangement is seen as newsworthy.
The family is split into two parts: The main family, which contains every first-born son, and the branch family, which contains everyone else. Kengo Moriyama heads the main family while his younger brother Tetsuji Moriyama heads the branch family. Because of this division, Ichirou Moriyama is part of the main family, but his brother Riko is part of the branch family. The main family is located in New York. The two parts of the Moriyama family are estranged, although the branch family receives a part of the profit the main family makes (legally and illegally). They have, however, no say in business decisions.
The main family uses the games of the Ravens as cover for big meetings. Using these covers, gives Tetsuji some power and he is still welcomed to the family by Ichirou, as seen as being invited to the funeral. However, he is dismissed once the Raven's reputation falls and comes into question.
The Moriyamas are known to have connections with people from every public force and have the means of power through their connections and money.
The Wesninkis serve the main Moriyama family. Nathan Wesninski (the Butcher) is a trusted member to serve the Moriyama family. The territory that the Wesninskis own is next to the Moriyamas, however these are also owned by extension by the Moriyamas.
The Moreau family owed the Moriyama family and were in severe debt. To repay the debt Jean was given to the branch family to be trained for court and would therefore eventually bring revenue for the Moriyamas.
Due to Mary Hatford's connection with the Butcher, Stuart Hartford is able to have some sort of contact with the Moriyamas. However, this is shown only to be after the deaths of Kengo and Nathan.