The Nikkyo Consortium (日侠連, Nikkyo-ren) is a subsidiary of the Tojo Clan.
According to Homare Nishitani and Tsukasa Sagawa of the Omi Alliance, the Nikkyo are the Tojo Clan's "Black Ops" group, operating behind the scenes to advance the Clan's general interests and specializing in assassination. The Nikkyo were apparently behind the killing of multiple Omi officers during the Omi-Tojo war of the 1980's.
Their main base of operations is a yacht which moves along Tokyo Bay at most times, but which periodically docks at Shibaura Wharf to refuel and receive maintenance. They also have a base in Osaka: a large brothel known as the Camelia Grove, from which they carried out most of their operations against the Omi during their war with the Tojo in the 80's.
In 1988, the Nikkyo's first president, Masaru Sera, formed an alliance with Captain Shintaro Kazama of the Dojima Family. Both men believed that Patriarch Sohei Dojima had become too powerful and needed to be reined in. At the time, Dojima sought to acquire a piece of land in the middle of Kamurocho known as the "Empty Lot", which would complete his ownership of the land that the city of Tokyo intended to buy out for the Kamurocho revitalization project. The owner of the Lot could use their rights over the land to oppose the revitalization project, which would not stop it completely but would delay it and make it drastically less profitable. If Dojima could consolidate ownership of all that land, he could sell it to the city at an exorbitant price and become wealthy enough to rule the entire Clan autocratically.
In order to stop Dojima, Sera kidnapped the Empty Lot's owner, Makoto Makimura, in Osaka and handed her over to Kazuma Kiryu and Jun Oda of the Tachibana Real Estate Agency, who worked for Kazama and intended to buy the land from Makimura in order to oppose the revitalization project from going through.
Afterwards, Goro Majima, who was trying to protect Makimura at the time, fought his way into the Nikkyo's Camelia Grove base and confronted Sera. After a rough battle, Sera revealed his alliance with Kazama and Makimura's whereabouts back in Tokyo.
After Makimura is shot by Dojima's assassin, Lao Gui, to stop her from opposing the revitalization project sale, Sera and his Nikkyo men raid Dojima's penthouse and rescue her along with Majima, taking her to a surgeon who works for them to be treated. The surgery is successful and Makimura is sent to the Nikkyo's Tokyo base to recover in safety.
Unfortunately for them, Dojima's new captain, Keiji Shibusawa finds the Nikkyo base and launches an attack on it to finish off Makimura and Sera. Before he is successful, they are interrupted by Kiryu, along with his oath brother Akira Nishikiyama, their mentor Osamu Kashiwagi and several men loyal to Kazama. Nishiki, Kashiwagi and their men manage to stop Shibusawa's men and Kiryu defeats Shibusawa in single combat, rescuing Makimura. Once she awakens, Makimura sells the Empty Lot to Sera, who threatens to oppose the revitalization project unless the Tojo Clan grants him control over the sale of the land to the City, to which the Tojo agrees, taking the deal away from Dojima.
Due to his acquisition of the Empty lot (and secretly due to his success in stopping Dojima's expansion), Second Chairman Takashi Nihara appoints Sera as Clan Captain and successor to the chairmanship; which he would eventually obtain upon Nihara's retirement in 1993.
In 1995, after being convicted for Sohei Dojima's murder, Kiryu is expelled from the Tojo by Chairman Sera, meaning that he is no longer part of the Clan but that he is pardoned for the murder of his patriarch. Regardless, a few days later, an assassin from the Nikkyo Consortium attacked him, claiming to be sent by Sera. Kiryu, however, managed to defeat the assassin.
After being released in 2005, Kiryu runs into the assassin again during Behind the Assassin; a substory exclusive to the Kiwami remake of the game. The assassin admits that it was the Second President of the Consortium, Masashi Kunieda, who had sent him, not Sera. Upon heading to Purgatory in order to find Kunieda, the president himself intercepted Kiryu, challenging him to a fight. Upon being defeated, Kunieda confirms he sent the assassin, but states that Sera had requested it of him. According to Kunieda, Sera ordered the hit to prevent other groups from trying to kill Kiryu, sending the message that Kiryu was "the Tojo Clan's burden". Kunieda also claimed that Sera deliberately dissuaded others from attacking Kiryu so that he could return to the Tojo once his sentence was completed.