Tokyo shares opened lower on Thursday after surging the previous day, despite gains on Wall Street following data showing another spike in consumer prices.
The benchmark Nikkei index fell 0.37 percent, or 107.44 points, to 28,658.22 at the open, while the broader Topix index was down 0.27 percent, or 5.38 points, to 2,013.98.
"Although caution over tighter US monetary policy eased, the market is likely to experience sea-saw trade due to the spread of Covid-19 in Japan," Mizuho Securities said.
But Okasan Online Securities said it was important that investors monitor surging virus cases "calmly".
Japan recorded more than 13,000 new infections on Wednesday, a jump from a few hundred cases per day in recent weeks.
"The increase in cases is expected, considering the large number of people going out during the year-end and New Year holidays, and the speed of contagion in Europe and the US," Okasan said.
The market was also weighed down by a stronger yen. The dollar fetched 114.65 yen against 114.53 yen in New York but down from 115.32 yen in Tokyo on Wednesday.
On Wall Street, the Dow Jones Industrial Average closed up 0.1 percent. The broad-based S&P 500 advanced 0.3 percent, while the tech-rich Nasdaq Composite Index rose 0.2 percent.
In Tokyo trading, Uniqlo operator Fast Retailing, which is scheduled to announce Q1 financial results later in the day, dropped 1.74 percent to 59,250 yen while market heavyweight SoftBank Group tumbled 1.14 percent to 5,618 yen.
Airlines were lower with Japan Airlines losing 1.27 percent to 2,166 yen and ANA Holdings falling 0.99 percent to 2,395 yen.
Nintendo slid 0.82 percent to 53,150 yen while Sony gained 0.44 percent to 14,585 yen.
Toyota was up 0.48 percent to 2,371 yen and Nissan climbed 0.66 percent to 636.1 yen.