The spread of the novel coronavirus may have slowed economies and closed many businesses worldwide, but it has not been a damper on a newly opened Tokyo sauna that caters to solo customers. The Finnish-style sauna rooms at Solo Sauna Tune, where customers can relax in solitude and enjoy the heat from water over hot stones, are so popular they are booked up within hours. Although the idea for the business came before the spread of the coronavirus, the pandemic and the social distancing it brought have been a big boost, said co-founder Daisuke Kawase. “We feel that there has been a strong demand for solo services like these as a way of preventing the spread of the coronavirus,” Kawase said. The sauna, which opened last week, also caters to a growing market of single people in Japan. According to government statistics made available in 2018, the ratio of single-person households in Japan is estimated to increase to 40 percent in 2040, from 30 percent in 2005.