Japanese shares fell on Monday, dragged down by a sharp decline in SoftBank Group (9984.T), while investors remained risk averse as worries over the omicron variant of COVID-19 persisted. The Nikkei share average (.N225) fell 0.6% to 27,870.05 by 0215 GMT, after opening 0.18% higher. The broader Topix (.TOPX) was down 0.48% at 1,948.43. "The market has been volatile and will be so as long as investors seek details on the Omicron variant," said Ikuo Mitsui, fund manager at Aizawa Securities. "But as for the Japanese market today, the declines are led by individual stocks, particularly SoftBank Group, which is facing multiple negative factors." SoftBank Group tanked 7.11%, losing half of its value from its year-high in mid-March, on concerns over the valuations of portfolios in which the global technology start-up investor in and its Vision Fund have invested. Didi Global (DIDI.N), which is 21.5% owned by Vision Fund, fell more than 22% on Friday after the ride-hailing giant said it would withdraw from the New York Stock Exchange and pursue a Hong Kong listing. read more Also, the U.S. Federal Trade Commission sued to block U.S. chip company Nvidia Corp"s (NVDA.O) more than $80 billion planned acquisition of British chip technology provider Arm, which is owned by SoftBank. SoftBank"s mobile phone company SoftBank Corp (9434.T) reversed course to edge up 0.2%, while Z Holdings (4689.T) , SoftBank Corp"s internet business, lost 2.81%. The Mothers Index (.MTHR) of start-up firm shares lost 3.66% Other major technology shares gained, limiting losses in the Nikkei, with phone company KDDI (9433.T) 1.18%, robot make Fanuc (6954.T) 0.3% and air-conditioning maker Daikin Industries (6367.T) 0.08%.