
Hiroaki Arai was a Japanese undercover police officer who infiltrated the Tojo-kai yakuza clan during the 2000s, rising to be Captain of Kanemura Enterprises by 2010. A protege of TMPD deputy commissioner Seishiro Munakata, he played a central role in Munakata and Isao Katsuragi's intrigues in 2010, although he eventually betrayed both in his quest to take control of the Tojo Clan and deliver his own brand of justice. He was ultimately defeated by Shun Akiyama and arrested for his crimes.
Biography[]

Arai in 2010
Hiroaki Arai was born in Tokyo, Japan, and he joined the Tokyo Metropolitan Police Department (TMPD). While he was strongly inclined towards delivering justice, he was highly ambitious and manipulative, and he also admired the yakuza and their code of honor, elements of which made their way into his own personal creed. During the early 2000s, his superior Seishiro Munakata assigned him to infiltrate the Tojo-kai, and he joined the Kanemura Enterprises subsidiary of the Shibata-gumi and became oath brothers with Takeshi Kido and a partner of Munakata's other underling, Isao Katsuragi of the Uenoseiwa-kai. In 2005, he defended the homeless man Shun Akiyama from "homeless hunters," causing the two to become friends. After Akiyama founded Sky Finance, he bankrolled Arai's rise within the Tojo Clan, as Akiyama had a positive, if false, perception of Arai's character.
By 2010, Arai became close to Katsuragi and Kazuo Shibata and learned the truth of the "Ueno Seiwa hit" of 1985. In March 2010, his conspirators had him murder Ueno Seiwa gangster Masaru Ihara at Club Elnard to nearly provoke a gang war, allowing for Katsuragi to issue the Tojo an ultimatum demanding Arai's head or thee Tojo's lucrative Kabukicho Hills project. Arai was secretly sheltered by Shibata on Katsuragi's orders, pressuring Tojo chairman Daigo Dojima to hand over Goro Majima's Kabukicho Hills development. Arai later resurfaced when Masayoshi Tanimura witnessed his murder of Shibata at the Tokyo docks after Shibata attempted to violate the captive Yasuko Saejima, who had murdered several Shibata officers under Katsuragi's orders. Arai revealed his loyalty to Katsuragi in front of a dying Shibata, a captive Yasuko, and a spying Tanimura, who then failed to make an arrest as Arai fled. As the situation became more desperate for the Tojo, Munakata arranged a meeting with Daigo and Arai at which he promised to help the Tojo crush the Ueno Seiwa and refill their coffers with police expropriations if Daigo would make Arai the new Captain of the Tojo Clan, hoping to clear a path for Arai to take over the Tojo.

Arai betraying Katsuragi
Arai was later approached by Kido, who planned to betray Katsuragi and steal back the ¥300 billion that Kido had himself stolen from Akiyama's secret vault. Arai and Kido betrayed Katsuragi when he handed the money and the Saejima siblings off to Kazuma Kiryu at Kabukicho Hills in exchange for an incriminating ledger, only for Kido to shoot Arai and leave him for dead before departing with the ledger. Arai returned the ledger to Munakata, who was implicated in embezzlement in the ledger's contents; however, Munakata reprimanded him for not retrieving the money, and ordered him to kidnap Kiryu's adoptive children from Okinawa to serve as bargaining chips for the money's return. A disgusted Arai shot Munakata and fled, although Munakata - who had feared Arai's own ambitions - had secretly replaced his bullets with police-issued rubber rounds, allowing him to survive Arai's betrayal. Not long after, Arai's suspicions about Kido were confirmed when Kido went back to his boss Dojima, who had sent him to steal the money for the Tojo.

Arai betraying Munakata
On the night of 15 March, Arai headed to the roof of the Millennium Tower when Akiyama let word slip that his ¥300 billion was stored there. There, he confronted Kido and Daigo, whom he accused of betraying the Tojo due to Daigo's selling out of Goro Majima. Arai also announced his disavowal of both the police and Daigo, intending on seizing control of the Tojo for himself and enforcing his own brand of justice. When Daigo accused Arai of treachery, Arai said that he had killed Munakata, only for Munakata to arrive with an elite police team and reveal that he had survived Arai's rubber bullets. Before Munakata could have his men execute the yakuza, a helicopter arrived and dropped off Kiryu, Tanimura, Akiyama, and Taiga Saejima, who picked foes to battle. Akiyama battled his old friend Arai, besting him in combat. Arai, accepting defeat, helped subdue Munakata and complimented Tanimura for his integrity. He then accepted that he should stay in prison for his crimes and also believed that Munakata should join him in prison, but Munakata shot himself before he could be arrested. Arai went on to serve time in prison for the murders of Ihara and Shibata.