The real-life inspiration for Daidoji, Yoshio Kodama, would be considered too unrealistic by fans
Yoshio Kodama is the most famous kuromaku (aka The Fixer) in the recorded history of Japan. Minoru Daidoji and the Daidoji Faction as a whole are loosely based off him and his activities. However, the real thing is... WAY more extreme than the fictional counterpart. Both in his crimes, and the scale.
Yoshio Kodama came from a bankrupt samurai family, spent his teenage years working a steel mill in occupied Korea, and returned to Japan as a member of the Gen'yōsha (Dark Ocean Society), an extreme-right secret society that became the first to group extreme right-wing and yakuza together. The founder of Gen'yōsha, Toyama Mitsuru, sent him to Manchuria, where he would be involved in the suppression of the anti-Japanese resistance.
In 1932, Kodama formed his own ultranationalist group, Dokuritsu Seinensha (Independent Youth Society), whose main activity was opium export from Japan to Korea and Manchuria, specifically to break the resistance of the local population against Japanese occupation by chemically suppressing them. His group was also responsible for assassinations of Japanese politicians advocating for the peaceful coexistence of Japan, Korea, China.
During WWII, Kodama ran the Kodama Kikan (Kodama Organization), an officially-sanctioned purchasing agency for the Imperial Japanese Navy that he ran as a persona lplunder operation. His forces extorted Chinese and Manchurian peasants at gunpoint, forcing them to sell metals, while he built a network of salt, iron, and molybdenum mines across occupied territory. The opium operation scaled up in parallel. By 1945, he had accumulated over $175 million, making him one of the richest men in Asia.
After WWII, he was arrested as Class A war criminal and thrown into Sugamo Prison. And then CIA bailed him out. All charges were dropped and he walked free on Christmas Eve, on the condition that he would suppress communist activity and conduct smuggling operations for CIA across Asia.
During the Korean War, Kodama negotiated directly with General Douglas MacArthur and supplied thousands of yakuza and former Imperial Japanese Army veterans to Korea, where they were deployed disguised as Korean soldiers. He was sending his private army to fight a foreign war under a false flag.
Post-war Japan had 184,000 yakuza spread across 5,200 gangs, a number larger than the Japanese army at the time. Kodama was the man who unified them. Through a mix of diplomacy, shared political goals, and intimidation, he brokered truces between the major groups, and in 1972 engineered the historic alliance between the Yamaguchi-gumi and the Inagawa-kai, Japan's two dominant yakuza organizations. The pact was sealed at Taoka's home in a traditional sakazuki ceremony. The resulting alliance left only four of Japan's prefectures outside their combined control.
Using his CIA backing and yakuza network, Kodama and his Sugamo Prison cellmate Nobusuke Kishi engineered the formation of Liberal Democratic Party. Kodama was responsible for funneling the funds into the party, with CIA's full support, on the basis of making Japan a bulwark against communism in Asia. LDP is the sole ruling party of Japan to this day, and many of the subsequent prime ministers were direct Kodama protégés. Shinzo Abe is Nobusuke Kishi's grandson.
When President Eisenhower was scheduled to visit Japan to ratify the US-Japan Security Treaty allowing permanent American military bases on Japanese soil, the Anpo protests paralyzed the country, with left-wing protesters opposing the treaty. Prime Minister Kishi called Kodama, who assembled the Zen Ai Kaigi, a federatio nthat included the founders of all three of Japan's major yakuza groups: Kakuji Inagawa of the Inagawa-kai, Yoshimitsu Sekigami of the Sumiyoshi-kai, and Kinosuke Ozu, "Tokyo's Own Al Capone". His mobilization plan promised over 146,000 men on the streets. The visit was cancelled when a student died in the clashes, so his army stood down.
Kodama had been a paid consultant for Lockheed for 15 years prior to the scandal, receiving $7 million for his services, plus a further $6 million commission for steering Japanese parastatal airlines toward the L-1011 TriStar. When it all came out in the 1970s and ended his career, a disillusioned ultranationalist porn actor named Mitsuyasu Maeno attempted to assassinate Kodama by flying a plane kamikaze-style into his mansion, dying instantly in the crash. Kodama was unharmed as he was in a different room at the time.