Bain didn't disclose how much it is paying to buy out shareholders in the company, include its current president. People with knowledge of the matter said Bain will pay about 50 billion yen ($422 million) for the company's shares and debt.
In a statement, Bain said Ooedo-Onsen sales have risen about 30 percent annually since 2007. Best known for its spa on the man-made island of Odaiba in Tokyo Bay, the firm expects to book revenue of about 35 billion yen for its fiscal year ending February from its 29 hotels and spas nationwide.
The deal comes as Japan seeks to raise the number of foreign tourists visiting the country, relaxing some visa regulations and extending the sale of tax-free items, as a way to boost the country's sluggish economy.
A record 13.4 million foreigners visited Japan last year, a 29 percent jump from the previous year, according to Japan National Tourism Organization. The government has set a target of 20 million visitors a year by 2020 when Japan hosts the summer Olympics in venues across the capital, including some close to Odaiba.