The Millionaire Detective Balance: Unlimited

Detectives Haru Kato and Shinnosuke Kamei from Japan’s Modern Crimes Prevention Task Force are asked to assist security during the Ginza Classic Car Festival where First Division officers are trying to locate a bomber targeting a foreign prince. Two amateur thieves, Yoko and Hiroshi, observe jewelry stores for a potential robbery. The ridiculously wealthy Daisuke Kanbe meets the Police Superintendent and requests a place on a squad of his choice. The bomber is arrested while the thieves accidentally rob a sweet shop, unknowingly fleeing the bombers' van with the bomb. During their pursuit, Daisuke inflicted damage on nearby vehicles and public facilities. Afterward, he immediately reimbursed all the repair costs with additional compensation money through his artificial intelligence assistant. The wealthy detective successfully pushes the van into the river to safely detonates. At the same time, Kato rescues the thief before falling into the river while an amused Daisuke watches.

A fashion model, Akiko Hoshida, dies of an overdose. Daisuke arrests two street performers for buying Mescaline and bribes them for their dealer’s name. They identify the model Isezaki as the dealer and witness him selling drugs, but Daisuke decides not to arrest him. They learn Isezaki's narcotics came from the organized crime group Gondawara Gumi, run by mob boss Umezu. Kato decides to follow Isezaki’s latest girlfriend, only to follow her to Daisuke’s mansion. He learns she is Suzue Kanbe, Daisuke's relative who was working undercover and has discovered Umezu is attending a party. Kato infiltrates the party and steals Umezu’s phone. He managed to escape the bodyguard with help from Mita, a journalist helping the investigation, and Daisuke, who has HEUSC purchase the building before attacking it with sleeping gas. The entire crime group is arrested for drug smuggling and murdering Akiko. Kato confronts Daisuke about his money abuse. Daisuke reveals he knows Kato was kicked out of Division 1 for accidentally shooting a suspect and now is psychologically unable to fire his gun. Furious, Kato leaves but is later told to attend a symposium on international crime in Hong Kong, with Daisuke.

Kato is brought to meet Daisuke and Suzue’s grandmother, who asks Kato to make Daisuke a good policeman. Kato becomes involved in an incident when a young man takes several music fans hostage. Kato’s former Division 1 colleagues arrive, causing him to have a flashback to the incident when he shot a suspect. Daisuke arrives, but rather than leave with him, Kato decides to stay and learns the man is streaming the incident live on Chaintube. Kato asks Daisuke to help, so Daisuke launches smoke grenades, and they infiltrate the train. Division 1 Chief Takei orders Kato to shoot the man. Instead, Kato has HEUSC hack the man’s emails and learns he aims to win prize money from Chaintube by reaching 10 million views so his sick sister can have surgery. The hostages, desperate to see their favorite band Yokorenbo’s last concert, attack, but Daisuke distracts them by paying to have Yokorenbo sing outside the train. Kato has a chance to shoot but hesitates, so Daisuke steps in and pays for the sister’s surgery himself. Takei, rather than being disappointed with the crisis over, praises Kato for a job well done. Kato is further surprised to learn Daisuke only helped because he trusted Kato’s judgment that the man wasn’t a real killer.

Kato asks Daisuke to find a child’s lost puppy with HEUSC. Daisuke realizes that having stormed out of his house in a bad mood, he forgot the earring he used to contact HEUSC and lost his phone. Kato leaves the child with local police before Daisuke reveals his lack of access to his money. Suzue panics after learning Daisuke is loose in public without HEUSC. Their grandmother thinks the experience will be good for Daisuke. Daisuke goes shopping with Kato and then to his apartment, where he shows a lack of basic life skills. Kato asks why Daisuke joined the Modern Crimes Taskforce, but Daisuke falls asleep before answering. Suzue stays up all night worrying about Daisuke surviving, and HEUSC jokingly claims Daisuke’s balance is currently Limited. In the morning, Kato spends all day looking for the dog. Daisuke appears with the dog, delighting the child, but secretly informs Kato he learned the original dog was killed by a car. Hence, the wealthy detective bought the dog’s identical sibling from the local dog breeder so the child couldn’t tell the difference. Unfortunately, he has to ask Kato to pay the breeder and to lend him train fare. Returning home, Daisuke shows his family Kato’s recipe for natto rice, which Suzue finds delicious despite the meal only costing 246 yen. HEUSC returns Daisuke’s balance to Unlimited.

The task force is assigned to protect President Alvarez of Poliador, as there are concerns terrorists want to kill him. Daisuke, however, attends the embassy as Alvarez’s guest. Alvarez wants the Kanbe family’s help to modernize Poliador but faces tough opposition from indigenous protestors. An infiltrator retrieves a package and murders the embassy chef to keep it secret. Kato and the taskforce befriend an elderly embassy janitor. Daisuke and Alvarez are sent to a safe room after the chef is discovered. Daisuke has HEUSC hack security cameras so he can observe. Kato chases the murderer fleeing the embassy while HEUSC retrieves footage showing the murderer planting a tear gas canister, designed by a Kanbe Group company, filled with VX gas inside the panic room with Daisuke and Alvarez and stealing the key, trapping them inside. Kato catches the murderer, who disposes of the key down a drain, hoping Alvarez’s death will prevent the dam from destroying indigenous land. He then commits suicide before Kato can stop him. Suzue crashes her bike and can’t make it. At the same time, HEUSC informs Daisuke that he cannot tell him how to disarm the canister; despite being a Kambe product, Daisuke doesn’t have the necessary clearance. Kato manages to save them, having realized the janitor had a secret spare key and had been using the panic room to hide his dirty magazines. Alvarez returns to Poliador while Nakamoto begins investigating the origins of the canister, unaware Daisuke is watching him through HEUSC.

Daisuke becomes suspicious of his lack of clearance to his own company. Nakamoto learns the Mizuo Company probably made the canister device and informed Kato he has investigated Mizuo before. They confront Imura, a Mizuo Executive, but are forced to leave when she starts recording them. Daisuke has HEUSC hack Imura’s electric car, forcing her to speed so he could arrest her. During her interrogation, HEUSC successfully hacks Imura’s laptop, only to suddenly inform a shocked Daisuke he lacks the clearance to access specific folders due to their connection to the Kambe Group. Kato is approached by Takei and Hoshino, his former Division 1 boss and partner, respectively, who are suspicious of Kambe. Nakamoto locates incriminating evidence against Imura’s son that Imura had covered up. Kato tries to talk to Daisuke but is advised to walk away or potentially lose his job. Nakamoto receives a similar warning from their boss, Kiyomizu, about losing his pension. Regardless, Nakamoto uses the evidence against Imura’s son to try forcing her to reveal how Mizuo is linked to the Kamb Group. Kato, unwilling to allow blackmail, has Imura released from custody. Unfortunately, her electric car is hacked again, causing the battery to explode, killing Imura instantly. Nakamoto accuses Daisuke of Imura’s murder. Kato learns from Kiyomizu that the last time Nakamoto investigated Mizuo, it was due to the murder of Sayuri Kambe, Daisuke’s mother.

Nakamoto and Takei investigated the potential murder of Sayuri Kambe by Shigemaru, Daisuke’s father. Nakamoto received no help from the Kambe family and instead stole a photo album from which a witness identified Shigemaru as the murderer. Police Director Saiki, Takei’s now deceased father-in-law, kept a close eye on the investigation. Nakamoto found a locker key in the album marked with the symbol for Adollium, a dangerous material Shigemaru had been researching. Takei located the locker while Nakamoto learned Shigemaru committed suicide, followed by the key being stolen from his desk. With Shigemaru dead and the key being stolen, the investigation was closed. Nakamoto now plans to reopen the case, and Takei labels Daisuke a suspect for Imura’s murder. Kato calls Daisuke, who admits he hacked Imura’s car, angering Kato so much he smashes his car through Daisuke’s front gate. Daisuke insists he is innocent and only interested in solving Sayuri’s murder. Takei is gassed in his vehicle and experiences vivid hallucinations of Imura accusing him of her murder, fearing for his own life if he didn’t sabotage the Sayuri investigation and tricking him into calling Director Saiki. He awakens in Daisuke’s home, the hallucination having being created by an advanced virtual reality headset to trick him into revealing who he was afraid of during the Sayuri investigation, his own father-in-law Director Saiki.

Daisuke explains that after Nakamoto accused him of Imura’s murder, he managed to convince him he was only interested in Sayuri’s murder. Nakamoto agrees to hold Takei in Daisuke’s mansion while they find out what Adollium is. Nakamoto explains that he never discovered Shigemaru’s lab's location, and now it no longer even exists in the Kambe Company’s records. Daisuke interrogates his grandmother, but she refuses to talk. Nakamoto infers from Takei’s fear that his father-in-law, Saiki, was murdered to cover something up. Takei has been afraid for his own life ever since. Suzue realizes HEUSC is actively hindering them by deleting information from the company servers. Kato discovers the lab in a Kambe owned mansion in the mountains, and Daisuke decides to infiltrate in secret. At the same time, Kato acts as a decoy outfitted with Suzue’s military gadgets. An intruder enters Daisuke’s house trying to reach Takei, just as Daisuke had hoped, only for the intruder to begin bypassing security using passwords belonging to Shigemaru. HEUSC shuts down Suzue’s supercomputer, and Takei begins to panic while Nakamoto appears unconcerned. Daisuke infiltrates the lab and finds security recordings proving Shigemaru is alive. Suzue confronts the intruder but is knocked out after seeing his face. Nakamoto also confronts the intruder, and Takei decides to finally confront him as well. Later Suzue wakes up to Kato and Daisuke and learns Nakamoto and Takei are both dead.

Daisuke resigns. Katsuhiro reveals Nakamoto owned two dice that were actually a transmitter and receiver, and he planted the transmitter on Shigemaru. Hoshino arrests Kato. The other members of Modern Crimes manage to avoid the First Division officer monitoring them and locating the transmitter signal while Suzue locates Shigemaru’s car. Kato informs Hoshino of Shigemaru’s survival, but Hoshino accuses Kato of murdering Takei for causing the incident that made him unable to fire his gun. Hoshino later finds Takei’s resignation letter and realizes Kato is telling the truth. Daisuke locates Shigemaru’s car and triggers a nerve gas trap, indicating someone planned to kidnap him. Suzue finds footage of Frantz Weinski, bodyguard to Thomas Matheson, an arms dealer, before HEUSC begins deleting the footage. Modern Crimes realize the transmitter is near Oura Wharf and inform Kato. Suzue sends an email to everyone in the city, offering ¥100,000 to everyone who takes pictures of their surroundings and uses all the photos to locate Shigemaru at Oura Wharf. Kato illegally boards the container ship Shigemaru is on, closely followed by Daisuke in an advanced underwater combat suit. Daisuke fights Weinski. At the same time, Shigemaru activates an Adollium antenna that destroys Kato’s phone and Daisuke’s suit. Weinski destroys Daisuke’s earring, cutting him off from Suzue, and starts beating him. Kato draws his gun to shoot Weinski but hesitates again.

Kato drops a shipping container between Daisuke and Weinski, allowing them to escape. Weinski refuses to chase Daisuke as his only job is to get the ship to Poliador, so Shigemaru pays him ¥100,000,000 to teach Daisuke a lesson. Suzue scans the vessel and notices the engine is unusually small for such a large ship, so she sends drones after it, narrowly helping them avoid an ambush. Suzue explains that Adollium is somehow powering the ship with zero exhaust emissions. Daisuke heads for the engine while Kato tricks Weinski by pretending to have fallen overboard. Reaching the engine, Suzue theorizes Adollium creates energy from seawater and could provide the world an unlimited supply of electricity or be turned into a weapon. Daisuke begins sabotaging the engine, but Weinski appears and stops him. Kato also arrives and tries to shoot Weinski but hesitates again until Daisuke encourages him to stop being a civil servant and be a detective. Kato finally shoots his gun, destroying the engine. Daisuke’s suit reactivates, and he defeats Weinski. Daisuke starts to arrest Shigemaru for murdering Takei and Nakamoto. Resisting the arrest, Shigemaru orders HEUSC to incapacitate Daisuke with the ship's laser cannons. As Shigemaru escapes, Daisuke and Kato deliver Weinski and his men to Hoshino, who is happy to see Kato appears to have returned to his old self. Daisuke and Kato thoroughly destroy the ship to hide the Adollium before tracking Shigemaru to the mountains' lab.

Daisuke discovers the data on Adollium in the lab while Kato finds an underground train leading to Daisuke’s mansion. Daisuke hands the data to Suzue before confronting his father, whose real identity is his grandmother’s butler, Hattori, who disguised himself as Shigemaru to deceive Daisuke. Daisuke encounters his grandmother, Kikuko, who admits she wanted to keep Adollium as a family secret so they could profit from it. Daisuke’s mother, Sayuri, wanted to broadcast Adollium's existence to the public, so Kikuko had Hattori assassinate her and, for years, has kept Shigemaru prisoner. Kato tried to catch Hattori, but the butler resisted; he then shot the policeman in the thigh. However, the wound is nothing comparable to the butler's severe injuries. The young police finally managed to catch Hattori, armed with the knowledge that the servant had orders not to kill Kato and the critical injuries he still suffered. Daisuke almost orders Suzue to release the data publicly but hesitates when Kikuko points out that Adollium could be used to create weapons of mass destruction. Kato, bleeding heavily, trips onto Suzue’s computer and accidentally releases the data anyway. Amused at the result, Daisuke arrests Kikuko. Two weeks later, a recovering Kato refuses an offer to return to First Division, preferring Modern Crimes, while Daisuke helps Shigemaru begin recovering. Modern Crimes become much more efficient after Daksuke gives them HEUSC. Meanwhile, with Adollium now becoming public, it changes the world dramatically. It even starts appearing on the black market with Daisuke and Kato working to prevent its power abuse. Stopping another black market meeting, Kato ends up once more falling into the river as an amused Daisuke watches, just like the first time they met.