SOGO group president Hiroo Mizushima paints a rosy picture for China's retailing business, but says Sogo has yet to join the ranks of other Japanese retailers such as Yaohan and Isetan in that market. Mr Mizushima said that while the retailing sector on the mainland was ''flourishing'', there were difficulties. He said that so far, no plans had been mapped out by Sogo in China. Mr Mizushima is in Hong Kong for the opening of the $2.5 billion Jumbo Sogo in Causeway Bay - the largest department store in Hong Kong - on Monday. Takuya Kawauchi, managing director and general manager of Sogo Hong Kong, yesterday said the $2.5 billion investment would take 15 years to pay back. With a total retail floor space of 360,000 square feet, the store will occupy the 10 lower floors and two basement levels of Sogo's existing premises as well as the company's new 22-storey building in Causeway Bay.