As strange as it sounds, it's the truth. In Japan, tattooing can only be done legally by a doctor, though up until the Osaka raids police had only targeted tattooists linked to the yakuza, Japan's powerful organised crime syndicates.
The unusual legal situation is due to regulations aimed at keeping permanent-make-up-style tattooists in check — the same health notice also listed laser hair removal and chemical peels as doctor-only procedures.
So it came as a shock to Japanese tattoo artists when police began using the law to raid ordinary studios, and arrest those working there.
"Tattoo artists who had no ties to anti-social organisations were being arrested," Masuda told the ABC.
"Some of them went to jail and had to pay fines to get out. So I was very alarmed."
On principle, Masuda refused to pay the fine.
"If I pay the fine, then I admit that I was guilty, and everyone will be at risk of getting arrested. So I decided to fight it," he said.
The 29-year-old's trial is now underway in Osaka, and his legal team has called on legal and historical experts to argue that tattooing is a legitimate enterprise in Japan.
Either way the trial goes, it's almost certain to set a precedent — but there are concerns a guilty verdict may encourage police across the country to conduct similar raids.
Criminals or guardians of tradition?
A national crackdown would be just the latest twist in the history of one of Japan's most taboo traditions.
Tattooing has been practised in Japan from at least the third century, and has been used for a variety of reasons — from branding criminals to tying lovers together, and even as talismans to protect men working dangerous jobs.
Firefighters' bodysuit-style tattoos often featured water-related themes like koi fish, dragons and waves.
Tattoos based off woodblock prints of folklore heroes became popular during the 19th century, and some of those characters were even depicted as having tattoos themselves.
But while tattoos were fashionable among young people and blue-collar workers, it was not a widely accepted practice among more highly educated Japanese, influenced by ideas imported from China.
The Confucian thinking was that tattooing the body was disrespectful to the person's parents, who created that body.
Japanese officials eventually banned tattooing in the late 19th century, and that remained in place until the end of World War II.
In the intervening period, yakuza members became some of the main customers for Japan's underground tattoo artists.
Despite this association, Brian Ashcraft, co-author of the book Japanese Tattoos: History, Culture, Design, is not convinced the reasons behind Japan's tattoo taboo have changed much over the centuries.
"I still think it's very much a class thing," he said.
"I think that people look down on tattoos, and they think that it's something that polite society doesn't do."
In a country that prides itself on its unique culture and history, there is a sort of irony in the stigma attached to tattoo artists and their craft.
Mr Ashcraft says they are some of the main custodians of the country's traditional art styles.
"These are artists that when Buddhist temples need stuff painted, they're going to sometimes call these people up to do it, because these are artists that are familiar with these designs and motifs," he said.
"These people who are very much guarding traditional culture are shunned by the greater society at large."
'Old values clashing with a new culture'
However, many of the tattooists arrested in the Osaka raids did not specialise in traditional tattoos, which are more often associated with the yakuza in Japan than Western styles.
"They represent a newer generation of tattoo artist," said Hyoe Yamamoto, a filmmaker who has been following Masuda's case for around 18 months.
He says the incident reflects a general unease over subcultures in Japanese society, which values social conformity.
"In Japan, everything depends on how you represent yourself, how you dress and how you behave," he said
"[Authorities] are now basically interfering with a culture scene, they're deciding what is supposed to be the legitimate culture or not."
The chasm between Japan's cultural norms and those of other countries has come into focus ahead of the upcoming 2020 Tokyo Olympic Games.
Japan's Government has recently been trying to loosen up laws and regulations that may cause headaches for the expected influx of foreign athletes and tourists.
The Government last year asked hot springs and bathhouse operators, which often reject tattooed patrons, to make allowances for foreigners by letting them use stickers or bandages to cover up before bathing.
In a more quirky pre-Olympics backdown, a decades-old ban on dancing at nightclubs after midnight was also lifted two years ago.
But Mr Yamamoto says young people are increasingly prepared to challenge Japan's social norms, and he sees Masuda's case as an example of that shift.
"It's old values clashing with a new culture," he said.
"This young kid happened to stand up just because he didn't feel that it was right. That kind of thinking itself is very representative of a younger generation."