Koichi Adachi (足立 宏一, Adachi Kōichi) is a one of seven playable characters appeared in Yakuza: Like a Dragon. He is a former police officer and driving instructor with the Kanagawa Prefectural Police. He uses the alias Yamada (山田) with Takashi Kusumi.
Adachi has a heavy, muscular build and graying, slicked back hair with a widow's peak. He wears a blue bomber jacket with a brown fur collar and the sleeves pulled up above his elbows over white T-shirt, a pair of fingerless black leather gloves, a silver watch, khaki pants, and a pair of lace-up sneakers.
Adachi is a driven man who carries himself with a nonchalant demeanor. Despite that, he holds deep care for his companions, and responds to stressful situations with intelligent planning and quick thinking. Adachi appears as a somewhat knowledgeable person, as his past career enables him to get the grips of the criminal underworld. Being a former police officer, he's able to piece together information that the party receives to form a solid hypothesis. However, on the flip side, he's terrible with money, as he admits to spend it on drinks and women.
Adachi was originally a police officer in Kanagawa Prefecture. In a case where he was investigating a robbery and double homicide of an old couple, he would come to arrest a man named Kusumi. Kusumi, who was innocent, was sentenced to 17 years in prison because Juro Horinouchi used witness intimidation to remove any alibi, as a false arrest would cause him a scandal. When Adachi tried to take action to expose Horinouchi, he was unreasonably demoted by him to the DMV and began work as driving instructor. Out of guilt, Adachi would send money to Kusumi's son Takashi under the alias "Yamada" after his parents died and he was sent to an orphanage, a decision which would cause Adachi monetary issues.
Yakuza: Like a Dragon: 2000-2019
Adachi first appears after Ichiban Kasuga is released from prison in 2019. Upon informing Ichiban that he knows about his false imprisonment, he insists that the two of them need to go to Isezaki Ijincho in order to uncover the entire truth surrounding the aforementioned incident. Kasuga, freshly out of jail, insists that Adachi stop digging around in the past, and leave him alone. However, Adachi insists on following Kasuga, and tells him about how the state of the yakuza world has shifted: The Tojo Clan having fallen, and the Omi Alliance taking its place at the hands of traitor Masumi Arakawa, Kasuga's old boss.
Refusing to believe such a thing is true, Adachi lets Kasuga go to Kamurocho to see for himself the changes that have taken place since his imprisonment. After Kasuga sees how drastically different things are in the city, Adachi meets back up with him, explaining that his superior, Juro Horinouchi had taken a bribe from the Omi in order to help wipe the Tojo Clan from Kamurocho, leaving it open for the opposing clan to move in and take their place. He wants evidence to arrest him and learn the truth of the Kamurocho 3K Plan that exiled the Tojo Clan. He gives Kasuga a cell phone and helps him break into an Omi Alliance officers meeting later that night, where the latter is shot by Arakawa, separating the two once again.
They meet up again when Adachi sneaks into Hamako's place to wake Ichiban, who is now accompanied by Yu Nanba. Adachi reveals that the stunt he and Kasuga pulled in Kamurocho led him to lose his job, and that the reason he's following the former yakuza around is to get revenge on Horinouchi, the three search for a job are are directed to Otohime Land. Initially wanting to leave due to the owner Nonomiya's comments to his workers, Nanba and Adachi decide to follow through after the soapland-raised Kasuga accepts. They drive off Bleach Japan protesting outside and are requested to investigate Nanoha Mukoda's suspicious behavior.
Adachi discreetly places his cellphone near Nanoha at a café and eavesdrop on her, learning she is to pay a large sum of money for her father Tatsuro Mukoda at Sunlight Castle. Kanbe helps the trio infiltrate by giving them contractor work, with Adachi being a security officer. They learn the facility is a pension scheme and Nonomiya requests they save Tatsuro and by proxy Nanoha. They agree and Adachi takes them to Survive Bar for a moment of rest. They steal a keycard, save Tatsuro, and confront the director Yamato Totsuka. They fight their way through Seiryu Clan headquarters to inform the chairman Ryuhei Hoshino of his underling's scheme and the captain, Mamoru Takabe, settles the issue with Nanoha afterwards. When they return to Otohime Land for their reward, they are met with the sight of Nonomiya's hanging corpse.
The three attend Nonomiya's funeral, where they first meet Nanoha's estranged twin Saeko Mukoda. Saeko states she heard the name "Lao Ma" being yelled when Nonomiya called her to inform her of Nanoha and Tatsuro, and the police ended their investigation after hearing her testimony. Adachi states Lao Ma is the nickname of a Yokohama Liumang boss, Akira Mabuchi. He also assumes the police ruled the death a suicide as they did not want to get in the Liumang's bad graces. Saeko tearfully asks the three for help, and they accept. They all head to Chinatown to ask about the Liumang, but this causes them to get assaulted. Saeko offers to work at a Chinese members-only cabaret they saw Zheng walk into. They enter and defeat Zheng, after which he tells them of Mabuchi's business operations and the Yokohama Trading Company, his largest business. Kasuga thinks they could get close to Mabuchi and decide to get jobs there the next morning through Kanbe. They head back, bringing Saeko along.
Being a former detective with years of experience under his belt, Adachi is well-versed in all manner close-quarters fighting. His "Detective" job has him use a makeshift police baton in combat which can double as a club. His default weapon is a Faded Police Baton that has lost it's shine from years of use. He can easily disarm people from their weapons in one fell swoop. Being the party member with highest health and defense next to Kasuga, Adachi naturally falls into the role of the resident tank of the party. Adachi has skills that can inflict "Rage" on his opponents, which allows him to influence enemy aggression towards himself to keep his fellow party members safe. He appears to use a southpaw Kali back stance, with his baton held in his left hand. His opportune strike has him thrust his baton downward into the enemy, and his default attack has him use an overhead swing with his baton.
- The given height of 190 cm (6′ 3″) is based on the character model's scaling factor within the game's data. For Dragon Engine games, this method is believed to be very accurate (±1 cm). However, this is intended as an estimate, not a substitute for an official statistic.
- Yakuza: Like a Dragon (Ryu ga Gotoku Studio, PC, November 2020) - .JSON File - "character_model_model_data.json"