Genzo is an older, balding man with sparse white hair whose face is lined with wrinkles. He is said to have had an old man's face even as a child, earning him the nickname "jii-jii" (old man) among his friends. In his old age, he insists that his face looks older than he really is, and true to his words, he retains some of the strength and speed from his youth.
In his younger years, Genzo was a famous killer who went by the initials "G.G." and was regarded as the best killer in Fukuoka. Thirteen years prior to the start of the series, he was badly injured and retired from killing. After his retirement, he opened the ramen stand Gen-chan and became a widely well-regarded mediator, receiving a variety of requests and handing them out to his numerous freelance killers.
Genzo also used to participate in Fukuoka's summer festival, the Hakata Gion Yamakasa, but old age and back pain have forced him to retire. He is still a fan of the festival and watches it every year.
Mayor Harada Scandal ArcEdit
Banba visits Gen-chan in the evening, and Genzo brings up rumors surrounding the Kakyuu Association and a recent request. He shows Banba a photograph from a security camera of Banba and Lin leaving Zhang's office and reveals that the Kakyuu Group has hired the Niwaka Samurai to kill them. Banba finds the situation amusing and tells an exasperated Genzo to go ahead and introduce the killer to the syndicate.
The following week, Genzo meets Saitoh, the Tonkotsu Ramens' new pitcher, and welcomes him to the team.
Niwaka Samurai Impersonator ArcEdit
When the Tonkotsu Ramens grasslot team falls far behind their opponents in a baseball game, Genzo suggests a punishment game. It inspires the other players to push themselves harder on offense. To help a worn-out Saitoh, Genzo steps into the batters box and pinch-hits. With all bases loaded, his home run puts the Tonkotsu Nine in the lead and ends the game with the Ramens' victory.
At some point, one of the killers Genzo mediates jobs to mistakes his target and kills the wrong man. Genzo cuts him off, but he has been blackmailing the mediator for consolation money. Abe and Yamamoto visit Genzo looking for work and overhear him mention the Niwaka Samurai on the phone. When he is finished with his call, he tasks the pair with assassinating the troublemaker. They mistakenly kill the wrong target, murdering Tadafumi Izuku instead. Abe devises a plan to find the original target again with Genzo's help, but Yamamoto tells Genzo of their blunder, and he immediately cuts them off. He quickly spreads word through his network of mediators, and no one in Fukuoka is willing to give the pair a job.
During his phone call before talking to Abe and Yamamoto, Genzo receives a request for the Niwaka Samurai. With Banba busy, Genzo calls Lin and gives him the job of protecting Yasukuni Shindou. When Lin fails and Banba completes his job of killing Shindou, the pair head to Gen-chan together for dinner. Genzo is chasing Yamamoto away from the stand as they arrive, and he forgives Lin for Shindou's death. When Lin recalls the conversation he had overheard earlier that day at Club Eve, he tells Banba and Genzo that the Kakyuu Group is looking to hire a killer named G.G. to take out the Niwaka Samurai. Banba dismisses this, but Genzo teasingly argues that the Niwaka Samurai is no match for the legendary G.G.
Several days later, Abe appears at Genzo's stall, and Genzo immediately refuses him work. Abe is visiting as a client, though, and faced with the enormous sum of money he offers for the Niwaka Samurai's time, Genzo agrees to consider the job. Banba is drunk and sleeping, however, and Lin takes the job. Shortly after, Jiro and Yamato visit Gen-chan and grumble about work. As they notice similarities in their story, they both take out photos of the same white van. Genzo recognizes the pair of drivers as his two former killers. He contacts the pair, promising more work, and Abe returns to his shop, allowing Yamato the chance to pickpocket his wallet and reclaim Kumiko Izuku's money for Lin. Genzo gives Abe a time and place to meet his next clients, where Jiro and Misaki are waiting.
In the early hours of the following morning, as Genzo is closing his ramen stand early to watch the final events of the Yamakasa festival, he receives an email from an unknown sender that contains images of a mutilated body resembling Lin's. He runs to find Banba and inform him, trying to stop Banba from retrieving Lin's body out of fear that the same might happen to another friend. Around dawn, Genzo calls Shinichi Saeki as he is patching up Lin's wounds. Genzo is relieved and elated that Lin is alive and well, and he informs Lin of Banba's attempts to retrieve his body and relates that he is unable to get in touch with him, causing Lin to go to the Kakyuu Association offices in search of him.
As Genzo is finally pulling his cart home later that morning, he is approached by Enokida and Saitoh, who are being pursued by a killer. Genzo knocks the killer down with a swift punch to the chest, and the three friends find themselves sympathizing with George Gondo after learning of his situation.
Shou Wang ArcEdit
Genzo leads the Ramens' weekly baseball practice and decides it is time to teach Lin the team's signs, stealing a run to second and sliding onto base despite his age. The next day, Lin visits Genzo's ramen stand alone, and after learning of the two Noriaki Hisashis murdered, runs off without paying. Banba and Enokida meet at Genzo's stand shortly after, where Enokida fills them both in on Feilang. When Banba receives a call from an injured Lin, Genzo agrees to help.
When thirty minutes has passed and Genzo has not heard from Banba, he assumes something has happened to him. He closes his shop and goes home to retrieve the clothing and weapons he had used in his assassination days. Picking up Enokida on the way, the informant leads them to the Kakyuu Group's headquarters. Genzo is able to get through to Banba's communicator as they get closer. He sets up explosives along the wall of the chamber Banba and Lin are trapped inside and detonates when the Ohori fireworks begin.
Genzo gives Banba his sword. With Enokida's grenades and his machine gun, he takes out the Kakyuu associates pursuing them, allowing Banba and Lin to go after Feilang. When the fighting is over, Genzo drives them all home.
Genzo hears the events of Saitoh's questioning with cybercrime investigators from Enokida, and he prepares ramen as he and Saitoh explain the situation to Martínez. He takes sympathy on a rattled and weeping Saitoh and treats him to ramen on the house. Later that day, Banba and Lin visit for dinner and ask him for work. He gives them each a job, and the following evening, Banba informs him that his target had committed suicide, proclaiming his innocence in a suicide note. They recognize similarities between Yusuke Aoyagi's supposed set-up and Saitoh's recent troubles, and Genzo gives Banba a new target, a hacker named Manabu Kuroiwa.
Later that night, Lin visits Genzo to asks him about Irasawa's habit of collecting spoils from his victims. Genzo has never heard of the teeth-collecting killer gives him a list of thirty other mediators in Fukuoka to call. The following evening, he treats Saitoh to another meal in celebration of Saitoh landing a company job.
Trusting Banba's judgment, Genzo quickly welcomes Lin to the baseball team and his circle of hitmen. He sees potential in Lin and teaches him tactics that he can use both in real life and on the field. He hosts team competitions and entrusts him with difficult or sensitive jobs in order to spur Lin's growth and to encourage him to trust in his friends. Genzo finds Lin amusing and cute, often siding with him and treating him like a grandchild.
- His contact information in Banba's phone is under the name "Old Man."