Takashi Nakamoto yells a friendly greeting from the kitchen when he spots a customer slide open the door to his restaurant, his face just visible through the steam rising from pots of stock and boiling water.

As he slices leeks and shakes the residual water from another batch of al dente udon noodles, it is easy to miss the most conspicuous physical reminder of Nakamoto’s life before he opened his restaurant, Daruma-ya, in the gritty southwestern city of Kitakyushu in June last year.

His missing pinkie is the legacy of three decades entrenched in Japan’s underworld, during which he rose from foot soldier to a senior position in the Kudo-kai, one of the country’s most violent yakuza crime syndicates.

After lunch service has ended, Nakamoto can be persuaded to lift up his T-shirt to reveal a tattoo stretching across his back and shoulders and down his arms. “That’s enough, it’s not for show,” he says in a tone that suggests the conversation move towards his extraordinary journey of self-awareness and redemption.

“Being a yakuza is not like working for a company or having a career – it’s a way of life,” he tells the Guardian over beers and sashimi at a nearby restaurant. “I was a real tearaway as a young man, so it felt natural to join the yakuza. I would do anything for my organisation. I was a serious gangster.”

It is no empty boast. Nakamoto’s years in the Kudo-kai were punctuated by stints in prison, including an eight-year sentence for his part in a violent attack on a Chinese-run massage parlour whose owners had set up shop without the gang’s blessing.

Now, though, the 52-year-old is one of a growing number of men who are cutting their yakuza ties to build new lives situated firmly on the right side of the law.

I joined the yakuza when it was at the height of its powers Takashi Nakamoto

His former gang, which has just over 600 members, is behind a string of violent crimes that violated the traditional yakuza code of sparing “civilians”. They include the murder of the head of a fishermen’s cooperative and hand grenade attacks on the city’s Chinese consulate general. In 2000, Kudo-kai members hurled petrol bombs at the constituency home of the prime minister, Shinzo Abe.

After a spate stabbings and shootings, in 2010 the national police agency designated the Kudo-kai as a “particularly nefarious group”. Residents took to the streets calling for the gang to be kicked out of their city-centre headquarters.

Takashi Nakamoto spent 30 years in Japan’s most notorious yakuza gang. Photograph: Noboru Aoki/Shinchosha

“Usually the yakuza doesn’t target women and other ordinary citizens, but the Kudo-kai was different,” says Masataka Yabu, who led Kitakyushu’s anti-organised crime division and now heads an organisation campaigning to end yakuza violence. “People wouldn’t testify or pass on information to the police because they were in fear of their lives.”

But two decades of stricter anti-gang laws and uncertain economic times have taken their toll on yakuza membership.

Members of the Kudo-kai, like those of other yakuza groups, no longer operate with the same near-impunity they enjoyed in the postwar years. Gang bosses can now be charged for crimes committed by their underlings, and local ordinances threaten to publicly name individuals and companied that do business with the mob. Repeat offenders face fines of up to 500,000 yen and company officials face up to a year in prison.

The battle to weaken organised crime is now being fought in the US, where the treasury department has blacklisted yakuza groups that use front companies to launder money and hide illicit profits.

“I joined the yakuza when it was at the height of its powers,” Nakamoto says. “It wasn’t about the money or expensive clothes and cars … we thought we were the epitome of the macho Japanese male, putting our lives at risk for our cause. No one wanted to mess with us.”

The yakuza gave the young Nakamoto – a high school dropout who barely knew his absentee father – the sense of belonging he had struggled to find in mainstream society. After mixing with gangsters as an estate agent, he joined the Kudo-kai, performing office duties, cooking for his oyabun boss, Hideo Mizoshita, collecting protection money and sourcing cheap labour for construction companies.

Nakamoto was in prison in 2008 when he learned that Mizoshita had died. His boss’s death, and pangs of conscience over the misery the gang had inflicted on innocent residents, led him to question his career choice and resolve to cut his yakuza ties for good.

He is now four years into a five-year probationary period, during which he is not allowed to rent property or open a bank account, but has at least found a career with long-term prospects.

A bowl of Takashi Nakamoto’s trademark udon noodles. Photograph: Noboru Aoki/Shinchosha

A 2016 survey of employers in Kitakyushu found that 80% would not want to hire a former yakuza. And ex-gangsters who manage to find work are likely to find themselves ostracised and discriminated against in the workplace, according to Noboru Hirosue, an expert in criminal sociology at Kurume University.

“For someone as senior as Nakamoto-san to quit the yakuza is almost unheard of,” says Hirosue, whose book about Nakamoto was published in July. “He had to put his whole life behind him and learn to be humble. He was once a wealthy man … he certainly isn’t now.”

Police and legal crackdowns are taking their toll on gang membership in Japan. The number of yakuza members fell to a record-low of 34,500 in 2017, down 4,600 from the previous year according to the national police agency.

In Fukuoka prefecture – home to the Kudo-kai and four other major crime syndicates – membership has declined to just over 2,000 compared with 3,720 a decade ago. To encourage more gang defections, local authorities recently started offering money to newly reformed men to help with their rent and travel expenses for job interviews.

“We have to keep encouraging yakuza to quit,” Yabu says. “They think they have a lot to lose, but when you remind them of the terrible things they have done they start to think again. Many of them want to go straight for the sake of their wives and children.

“Real-life yakuza are nothing like the honourable men you see in films. They receive good publicity for, say, handing out food and water after a major earthquake, but there is no such thing as a good yakuza.”

Nakamoto is grateful to other businesses in the neighbourhood for seeing him through his difficult transition from senior gangster to humble restaurateur. “The people around here have encouraged me a lot, especially when I felt like quitting,” he says.

“But the odds are stacked against people like me. It’s not as if I stopped being a gangster and then became just like everyone else. I’m not starting from zero … I’m starting from minus.”