(Bloomberg) — A retail investor buys shares in a small company, touts his position on social media and inspires a horde of followers to do the same. The stock price goes to the moon — before crashing back to earth.It’s an all-too-familiar tale to anyone watching the market in 2021, but this wasn’t GameStop Corp. It wasn’t even in America. And it happened in 2018.It was in the Japanese city of Osaka, where a day trader who goes by the nickname Tonpin was betting on a tiny maker of precision dies and molds called Nichidai Corp. and broadcasting the fact on Twitter, where he has more than 55,000 followers. The stock surged more than sixfold in the first three months of 2018 before losing most of the gains.The person behind the nickname was Toru Yamada, a former money manager, and he and another man have just been arrested for market manipulation, according to Japanese media reports. He wasn’t arrested for talking the stock up on Twitter, but on suspicion of trying to keep the share price down — albeit so it would have margin-trading restrictions removed which, when it happened, caused the shares to soar to new highs.The incident shows how regulators sift through unusual trading patterns and come to conclusions often years later. It may pique the interest of protagonists and observers of the recent meme stock rally in the U.S., such as users of the Reddit forum WallStreetBets.Yamada has yet to be charged, and it’s not clear whether he will be. And while nobody is suggesting that U.S. traders employed similar tactics to those he’s alleged to have used, the case illustrates the risks that can be associated with becoming a high-profile investor on social media. While you’re in the public spotlight, you may also be in the regulators’ crosshairs.“Everyone’s going to be on tenterhooks,” said Taketsugu Agari, the investor known as Takezo on Twitter, where he has almost 100,000 followers. “People don’t know what’s right and wrong,” he said. “People don’t know the rules.”Calls and direct Twitter messages to Yamada went unanswered. The Osaka District Public Prosecutors Office declined to comment. The Securities and Exchange Surveillance Commission, Japan’s market watchdog, wasn’t immediately available to comment. Prosecutors didn’t make clear if the men had admitted or denied the charges, according to local media reports.A regulatory filing shows that Yamada’s first disclosed purchase of Nichidai shares was Dec. 8, 2017, and he gradually increased his stake. By the time he first tweeted about it, on Feb. 1 the next year, the shares had almost tripled.That March, Yamada and another man placed a large number of sell orders below the market price just before the close, according to the media reports. Their intention was to keep the share price below a certain level to ensure restrictions on new margin trades on the stock were lifted, the reports said. The stock was released from the measures, and surged as much as 18% on March 12 when it next traded.In a tweet on March 10, Yamada appeared to discuss this process, showing screenshots of Nichidai trades just before the close, though it’s unclear if they were his trades.Separate from his arrest, Yamada has had many clashes on Twitter over the years about his discussions of his investments.“The authorities need to put some regulations in place,” Soichiro Iwamoto, a longtime trader whose firm advises new investors, said in an interview, talking about the practice of talking up stocks on social media. “Investors here don’t have enough financial literacy.”Others wondered what exactly Yamada had done wrong.“It’s amazing that selling to release the margin restrictions is treated as market manipulation,” Akira Katayama, a well-followed day trader known as Gogatsu, wrote after his arrest.Japanese retail investors have been advocating the country’s thousands of thinly traded stocks online for more than a decade, starting off on the bulletin boards popular in the mid to late 2000s before moving to Twitter, the dominant platform in recent years.The most prominent came to be known as “locust lords” for attracting a swarm of day traders. Yamada became the latest of the lords to go quiet in June, when he said he was taking a break from Twitter after his account had been briefly locked.Okansanman, an anonymous account with more than 175,000 followers that was famous for its rapid delivery of breaking news, went dark in early 2019 and hasn’t resurfaced.The Mysterious Twitter User Drawing a Swarm of Japan TradersYamada worked at two Chinese government-related funds before striking out as a day trader in Japan in 2013, he told Bloomberg News last year. He divided opinion on Twitter even before his arrest, with dedicated followers who mimicked his trades and others who accused him of being a manipulator, using his influence to pump up stocks before dumping them.“When many Japanese people lose, they want to blame it on somebody else,” he said last year, brushing off his critics.Followers may have to wait to learn of Yamada’s fate. Under Japanese law, he can be detained for as long as 23 days before charges are pressed.Meanwhile, many of his counterparts in the country who like to discuss stocks are moving from Twitter to other venues, including encrypted messaging apps such as Line and newer platforms like Clubhouse, according to the investor Agari. That makes it harder for regulators to monitor, he said.Read more: GameStop Frenzy Is Lost in Translation for Japan’s Day TradersAs for the fallout from the GameStop saga, that’s anyone’s guess. If the Japanese experience is anything to go by, any regulatory actions could be a long time coming, if they materialize at all.“This has been going on for over a decade, back from when people used to use bulletin boards,” Agari said, referring to retail investors talking up stocks online. “America is starting to look like Japan.”(Updates to include more details)For more articles like this, please visit us at bloomberg.comSubscribe now to stay ahead with the most trusted business news source.©2021 Bloomberg L.P.