Zenji Banba (馬場善治, Banba Zenji) is a private detective who runs his own detective office in Hakata and works closely with Shigematsu, Enokida and Saeki.
Banba is described as a tall, lean man usually dawning a white sweater with old jeans. The novels describe him as having messy, unkempt, black hair and brown eyes however, illustrations show him with dark brown hair. Despite his noted height, he is usually hunched over.
Banba has a gentle and laid-back personality, usually not caring for his appearance or the cleanliness of his residence, much to Lin's annoyance. He is usually patient and understanding in most scenarios, but when it comes to baseball he can be overbearing, especially to the novice of their team, Xianming Lin.
Light Novel Volume 1 Edit
Banba meets with Shigematsu in Kego Park, who informs him of the recent death of his colleague, Takeda. While it was officially ruled a suicide, the two conclude he was most likely killed for investigating Mayor Harada and his connections. After Shigematsu gives Banba a photo left behind by Takeda, he asks him to figure out the circumstances behind the detective's death. The photo shows the Mayor in the company of two unknown men and a woman. Suspecting the woman in the photo to be a killer, Banba decides to consult with the informant, Enokida.
He learns that the woman with the mayor is Reiko Asakura, an assassin and former Murder, Inc. employee, who specialises in killing people with poison. However, Banba points out that it is unlikely she was responsible for Takeda's death, and asks Enokida if he can dig up any information on anyone who specialises in strangulation. With this, Enokida swiftly pulls information on another former Murder, Inc. employee, Hisashi Ivanov. Before Banba leaves, Enokida gives him a GPS-equipped redback spider model listening device.
On his way home, Banba runs into Yamato and ends up questioning him about the people pictured with the mayor. Yamato recognizes one of the men in the photo as Takashi, an employee of a club called Miroir, so Banba heads there in an attempt to find out more. However, when questioned, the manager claims to not even remember if the mayor had ever been there. Banba is confident he is lying and leaves knowing he succeeded in confirming their relations and catching their attention.
After updating Shigematsu on the situation, Banba returns home to find himself being greeted by an unexpected visitor - a hitman named Xianming Lin, who came in order to protect him from other hitmen the Kakyuu Group will send. He explains that while he had originally been sent to kill Banba, protecting him was his way of getting back at his employer over a disagreement. Since Banba decides to humour Lin by staying inside and out of harm's way, he gives Lin the task of going out to buy some mentaiko. After returning to the office, the two of them eat some tonkotsu ramen and watch a baseball match.
The following morning, Banba leaves the office while Lin is sleeping and meets up with Enokida in order to find out more about Lin. After retrieving this information, he returns home to find Lin, who has tied up a killer dispatched by the Kakyuu Group. After letting him go, Banba offers Lin money for information. When Lin agrees, Banba interrogates him and learns that the other man in the photo with the mayor is Zhang. Lin takes the money and leaves.
Later that day, Banba tracks down Lin with the redback spider model listening device he put on him earlier and arrives at the Kakyuu office shortly after Lin kills Ivanov. Then after retrieving Ivanov's cell phone, Banba attaches the listening device to Ivanov's collar. He then leaves with Lin, who, due to his wounds, loses consciousness. Banba takes him back to his office.
Not long after Lin regains consciousness, Shigematsu arrives at Banba's office with information about the man suspected of murdering Qiaomei Lin, Takuya Itou (Saitoh). But having not really learned anything new and agreeing that Itou had nothing to do with it, Banba accepts Lin's request to locate Qiaomei's killer and asks for five years worth of mentaiko as payment.
Enokida arrives to share his findings into the killers hired by the mayor. He shows Banba and Lin the footage from the surveillance cameras at the hotel Takuya Itou was staying at, revealing he was set up by Reiko and Munakata. Enokida plays them the recording from the bug Banba planted on Ivanov's body and hear of Yusuke Harada, the likely culprit of Qiaomei's murder. Lin formulates a plan to have himself be sold to Yusuke as a woman trafficked by the Kakyuu Group in order to kill him and asks for Banba's and Enokida's help.
After taking Lin back to his office, Banba pays a visit to Genzo, who is a killer agent. Genzo tells him that a request to kill both him and Lin came in from the Kakyuu Group, who have hired the Niwaka Samurai to carry out the job.
Banba then heads to Saeki's cosmetic clinic, where he makes an offer to buy a body which had just been dropped off by Jiro. Since Jiro is still at the clinic, Banba asks him to avenge Qaomei's rape and death and lets him know that Yusuke is the culprit. Meanwhile, Enokida arranges the meeting between the mayor's people and Banba and Lin. By this time, the Niwaka Samurai has already been to the Kakyuu Group office to accept his assignment from Zhang.
As planned, Banba meets with Lin, disguised as a Kakyuu Group broker. He gives Lin a redback spider model device and a microphone to call him in case of trouble before having Lin hide in a suitcase. Banba goes to the meeting and the suitcase with Lin inside is transferred to a car trunk.
When Lin is faced with Zhang and realizes he has been set up by Enokida, he calls Banba for help through the microphone. But at that moment, the Niwaka Samurai appears holding what appears to be Banba's head.
Despite being ordered to behead Lin, the Niwaka Samurai beheads Zhang, kills his men, Shinohara and finally Munakata. He then removes his mask and reveals himself as Banba. He explains to Lin how he bought Shota's head and asked for Jiro's and Saeki's help to make it look like his. Shigematsu arrives to clean up the crime scene and Banba and Lin leave.
They go to Yusuke's apartment building where they meet with Jiro and Saitoh. Banba is wearing the Niwaka Samurai mask again. He waits for Reiko to call Munakata's phone, which he had retrieved earlier, and introduces himself as the Niwaka Samurai. He also informs her he killed Munakata and is coming for Yusuke. Reiko decides to run away but is caught by Jiro.
Banba and Lin enter the apartment and look for Yusuke, who hides and ambushes them with a gun. Saitoh throws a baseball at him and incapacitates him.
Some time later, Banba and Lin go to a warehouse where Yusuke is kept bound to a chair. Banba, wearing a Niwaka Samurai mask, interrogates Yusuke while Jiro records his confession, which is later used to overthrow the mayor. Banba and Lin leave before the avengers start torturing Yusuke.
Some time later, Banba convinces Lin to join the Hakata Tonkotsu Ramens baseball team despite Lin not knowing anything about baseball.
- He comes from Hakata and speaks in the local dialect.
- His favorite food is Hakata tonkotsu ramen and mentaiko (another Hakata specialty).
- He is a huge baseball fan and his favorite team are the local Fukuoka Hawks. He uses their theme Iza Yuke Wakataka Gundan (いざゆけ若鷹軍団) as his ringtone.
- He is the second baseman for the Hakata Tonkotsu Ramens baseball team.
- He owns a Mini Cooper described as red with a white line in the light novel.
- It is shown as blue in the first anime trailer but is red in the anime itself.
- He knows little about technology and owns a few years old cellphone instead of a smartphone.