The speculative frenzy in bitcoin is spilling over into the Tokyo Stock Exchange. Remixpoint Co., Infoteria Corp. and Fisco Ltd., have all seen volatile swings in their share prices after announcing businesses related to digital currencies.

Remixpoint, which has more than doubled since tying up with Peach Aviation Ltd. to let customers pay for tickets with bitcoin, fell as much as 9 percent in Tokyo on Tuesday.

Infoteria, up more than 50 percent in the past month, is testing ways to let shareholders vote by proxy using blockchain, bitcoin’s underlying technology. Fisco, a financial information services provider, began operating a bitcoin exchange last year and is up about 25 percent since early May. Infoteria declined 3.7 percent while Fisco was down 2 percent.

All of these gains coincide with bitcoin’s rally, with the value of the virtual currency doubling against the U.S. dollar since early May. That has made the stocks of the these small-cap companies an attractive way for speculators to invest in cryptocurrency markets without buying them directly. That’s because investors can make bets via their brokerage accounts instead of taking risks with bitcoin exchanges, according to Naoki Murakami, a well-known day trader in Japan.

“From about a month ago when all these virtual currencies started spiking like crazy, we began seeing the so-called ‘stocks of the virtual currency bubble,”’ said Murakami, a frequent speaker at investor conferences. “Not everyone is sure they can trust bitcoin exchanges. And some don’t have accounts there. That’s why they’re using the stock market to speculate.”

It’s probably not a coincidence that Japan’s stock market is being seen as a proxy for bitcoin investments. In April, Prime Minister Shinzo Abe’s government legalized digital currencies as a form of payment and placed rules around audits and security. That lent credibility to digital currencies, leading to some Japanese companies seeking partnerships with bitcoin startups.

Remixpoint is the biggest of the bunch, with a market value of 31.3 billion yen ($283 million). Remixpoint was the second-biggest gainer in the TSE Mothers Index over the past month, helping the gauge soar to the highest level in a year. Remixpoint is trading at 514 times earnings, the highest among all Japanese technology companies worth more than 30 billion yen.

Another reason why these stocks can become proxies for bitcoin is due to Japan’s relatively loose listing laws, some of which require no income and a market value of as little as $10 million before a company can go public. That’s made the Tokyo Stock Exchange home to hundreds of small companies.

“It’s pure frenzy,” Murakami said.