Oishi is a character in Yakuza 0. He appears as a minor antagonist in the game, serving as a lieutenant of the Kijin Clan, a group that Goro Majima comes into conflict with when they try to kidnap Makoto Makimura.
Oishi is a lieutenant in the Kijin Clan, under its Patriarch, Homare Nishitani. In 1988, Keiji Shibusawa, lieutenant of the Dojima Family, employs the Kijin Clan to kidnap Makoto Makimura in Sotenbori since, unbeknownst to her, she was the owner of the Empty Lot in Kamurocho that the Dojima Family was desperate to acquire. On Nishitani's orders, Oishi sets about tracking down Makimura.
He manages to find her in Hogushi Kaikan Massage, where she works for Wen Hai Lee. The Kijin lieutenant and his goons arrive just as Lee and Goro Majima are in the middle of a fight over Makimura. Oishi shoots and injures Lee but is unable to defeat Majima, who runs off with Makimura.
A humiliated Oishi is beaten by Nishitani for his failure and tracks down Majima to his place of work, the Cabaret Grand. When he tries to threaten Majima into revealing where he'd hidden Makimura, he is promptly beaten up once again.
Oishi's final appearance occurs when Nishitani decides to take the kidnapping into his own hands. The Kijin Patriarch rented out the entire Cabaret Grand and called Majima to meet him there to try and bribe him into giving up Makimura. When Majima shows up to meet with Nishitani, a visibly bruised Oishi welcomes him at the entrance and sheepishly invites him to meet with his boss.