by Karpeles, while bitcoin itself - free of any central bank control - was still a noble venture.
"If we could agree on legal regulation, we should let (bitcoin and regulators) co-exist," said Keiichi Hida, a bitcoin investor and member of the Japan Digital Money Association. He lost about 100,000 yen worth of bitcoins, but seemed unconcerned as he became interested in the virtual currency as a form of "study".
"We should make it a national project to have bitcoin used nationwide at the time of the 2020 Tokyo Olympics," he said.
Mt. Gox shut its website on Tuesday after freezing withdrawals earlier this month in the wake of a series of technical difficulties.
The exchange had liabilities of 6.5 billion yen, dwarfing its total assets of 3.84 billion yen, the company said. It had 127,000 creditors in bankruptcy, just over 1,000 of whom are Japanese.
The company and Karpeles have said little in the days before Friday's court filing, which is similar to Chapter 11 bankruptcy in the United States, except that they were working with others to resolve their problems.
Another lawyer, Akio Shinomiya at Yodoyabashi and Yamagami, said Mt. Gox wanted to file a criminal complaint against what he said was a hacking attack, but had no specific means of doing so.
"Bitcoin has always been volatile and speculative, said bitcoin user Ken Shishido, who had about a tenth of his bitcoin holdings at Mt. Gox, but has seen the rest of his bitcoins soar tenfold since he began trading 18 months ago.
"It's too bad that this happened, but we have to let it go. And then we'll buy more."
Fortress Investment Group became one of the first big investors to say it had lost money investing in bitcoin. In a regulatory filing with the U.S. Securities and Exchange Commission, the company said it incurred $3.7 million in unrealized losses in 2013.