In a city known as Fukuoka, crime exists in the underworld from a seemingly peaceful surface. In the Hakata ward of the city, there are various individuals with special talent that consists of professional killers, detectives, informants, and professional revenge seekers. Furthermore, according to an urban legend, an individual known as "killer of professional killers" has shown up in the city.
Saito is a rookie at a contract killing company, has been demoted to a post in Hakata, a highly competitive market for hitmen. Banba, a private investigator, is asked to look into a detective's apparent suicide. The detective has left behind a photo of the current mayor of Hakata, the subject of many a dark rumor. Meanwhile, Hayashi, a cross-dressing hitman in the employ of a criminal organization, is in Zhang's face demanding more money. His employer shows him a business card as a potential target, but...
Hayashi had seemingly snuck into Banba's office to kill him, but Hayashi intends to protect Banba from hitmen in order to get back at his employer, Zhang. Meanwhile, Saito narrowly avoids being tortured and killed due to a case of mistaken identity by Jirou and Misaki. Celebrating his good fortune with a night of revelry out in town, Saito awakens from a drunken stupor in a hotel room to find the body of a woman he's never seen before lying next to him.
Saito has been blamed for a murder he did not commit and hires Jiro to get revenge on the real murderer. Meanwhile, Lin learns that his sister who he left in his hometown was killed in Hakata and confronts the killer’s employer Zhang. Blinded by rage, Lin is taken by surprise by one of Zhang’s assassins and seriously wounded. Banba the detective arrives to help Lin and pledges to help find his sister’s killer.
Working with Enokida the information broker, Lin establishes that his sister’s killer is the Mayor’s son Yusuke. Having obtained information about the next human trafficking deal, Banba and Lin form a plan. Lin will pretend to be merchandise and attempt to reach the killer. But the enemy learned of their plan. Lin’s last ray of hope Banba is brutally killed by someone known as the killer of killers. Lin now finds himself in a difficult predicament.
The Yamagasa Festival, one of the three biggest festivals of Hakata, is in full swing. Banba, born and raised in Hakata, is taking time off work to celebrate. The ace assassin of a contract killer agency Saruwatari has developed a distaste for work he does not find challenging. He decides to quit and move Hakata where there is more competition. As soon as he arrives, Saruwatari’s partner from high school Nitta calls out to him. Nitta works as an assassination consultant and wants to utilize Saruwatari’s skills, but...
Saruwatari craves a strong opponent and someone proposes going after the best assassin in Fukuoka, the Niwaka Samurai. Immediately after, the phone rings Banba’s agency, but because he is at the Yamagasa Festival, Lin pretends to be the Niwaka Samurai and goes to kill Saruwatari. Forced to use weapons he isn’t used to fighting with, Lin quickly gets into trouble. Meanwhile, Banba has just gotten wind that Lin took a job while claiming to be the Niwaka Samurai.
Information is the second most important thing to money. A cyberterrorist cell wants to find a hacker who has uncovered some sensitive details. Meanwhile, Banba Private Investigations receives a request to find a person. They receive a photograph of a boy with an odd haircut who disappeared eight years ago. Thinking he looks familiar, Banba and Lin turn to each other just as Enokida the information broker walks in.
Targeted by a “hacker hunter,” Enokida is forced to run from place to place in Hakata. Assassins after the bounty on his head are steadily closing in, and Enokida has been cut off from using computers, his only weapon. He’s fallen into a desperate situation. Meanwhile, Banba receives a message from Enokida. It’s a desperate counter to the cyberterrorist cell which came to Banba and Lin.
After a life of cruel wandering, Lin has found a place to be. The good-natured Banba has invited him to join his team of private investigators as well as his baseball team, the Hakata Tonkotsu Ramens. Lin is slowly learning to feel comfortable, but still has a lingering feeling that it won’t last. He remembers his harsh past. He was being raised as an assassin, and the first partner he met was...
Banba and Lin have decided to clean out the Kakyu Association executives from Fukuoka. Meanwhile, Nitta is negotes with an organization vying to gain a foothold in Japan. It’s an opportunity for Saruwatari to become their exclusive assassin. As a condition of the agreement, Nitta is asked to eliminate Kakyu Association executives… With their executives being killed, the Kakyu Association brings in a capable assassin from the mainland. That assassin, calling himself Fei-Lan asks only for the association to find someone as his compensation.
Employed by the Kakyu Association, Fei-Lan begins to seek revenge on assassins. His first target, Saruwatari can holds his own in a fair fight, but is taken by surprise. Meanwhile, Lin has run away from Banba and is hiding in Enokida’s internet cafe. There, Lin hears about the murders of two men both named “Hayashi Noriaki.” The men wrote their name the same way as Lin, both lived in Fukuoka and were killed one after the other. Realizing that the murders are a message for him, Lin goes to confront Fei-Lan and his past.
Confronting his past, Lin goes to see Fei-Lan, but fails to convince him to stop. Fei-Lan attacks Lin, but unsure if he wants to fight back, Lin becomes cornered. Banba arrives to help, but they are both unfortunately captured. Locked in a cage, Fei-Lan orders them to fight to the death and the winner will go free. Facing the same choice from his past, Lin must choose between killing and being killed.