The Kijin Clan (鬼仁会, Kijin-kai) are a yakuza group and subsidiary to the Omi Alliance.
The Clan main base of operations was a police precinct in Osaka, since Nishitani had paid off all the officers there to protect him and his men from attacks by any rivals. In order to cover for this, Nishitani and his men were simply "arrested" and brought to the holding cells in the precinct's jailhouse basement every time they needed to access their hidden offices. This arrangement was facilitated by Nishitani's uncle, Detective Billiken, who was the lead detective within the precinct.
The Kijin Clan and Billiken also operated the Bed of Styx, an underground fighting coliseum beneath the Sotenbori river where dangerous criminals were allowed to fight each other to the death in exchange for a chance at freedom. Much like the Purgatory underground coliseum which would later be established in Kamurocho, large crowds would gather at the Bed of Styx to bet on the results of fights, generating great income for the Kijin Clan.
In 1988, the Kijin Clan were hired by Keiji Shibusawa, lieutenant of the Dojima Family, to kidnap Makoto Makimura, a blind massage therapist who happened to be the owner of the Empty Lot in the middle of Kamurocho which the Dojima Family were desperate to obtain. Lieutenant Oishi was sent by Patriarch Nishitani to kidnap her from her job at Hogushi Kaikan, but he was thwarted by Goro Majima, who was also in search of the woman.
Impressed by his lieutenant's description of Majima, Nishitani himself tracks him down to his club, the Cabaret Grand, and challenges him to a fight. He is ultimately beaten and "arrested" by some of his police officers. Majima later tracks down Nishitani to his jailhouse headquarters in an effort to track down Makimura, who'd been taken by Masaru Sera of the Nikkyo Consortium. After Majima defeats him again, Nishitani offers him a chance to join the Kijin Clan, which Majima turns down.
Unfortunately for him, Nishitani is then betrayed by one of his bribed police officers, who'd been paid off by Shibusawa to take out Nishitani due to his failure to capture Makimura. The treacherous police officer kills Billiken and then shoots Nishitani, who manages to beat the officer to death before dying from his wounds.
It is unknown what became of the Kijin Clan after Nishitani and Billiken's deaths, as they were no longer amongst the Omi Alliance's top organizations by 2006.