Bargain hunting in large caps like Toyota Motor Corp offered some support and helped the benchmark Nikkei trim earlier losses.
The Nikkei average was down 0.1% at 13,944.43 at the midday break after falling as low as 13,885.22, its lowest level since October 9. It is down 15% so far this year.
The index shed 7.3% last week, its biggest weekly fall since the week after the March 2011 earthquake and tsunami.
Last week's slide has made some large caps relatively cheap, with Toyota now trading at below 10 times its earnings. Some technical indicators also signalled a chance of short-term rebound, with the Nikkei's 14-day relative strength index near 30, which marks oversold territory.
"Dip-buying in some large-cap stocks is supporting the market," said Yasuo Sakuma, portfolio manager at Bayview Asset Management.
Toyota jumped 3.3% and was the second-most bought stock on the main board. Mitsubishi UFJ Financial Group Inc gained 2.3%.
The Topix Core 30, which consists of large-cap shares, rose 0.8%, led by gains in banks.
"However, it doesn't mean the market is turning bullish. There appears to be selling in mid- and small-cap stocks from long-only mutual funds. Many market players are sitting on the sidelines for now, waiting for cues from annual earnings guidance," Sakuma added.
Japanese companies are due to report earnings later this month.
Indeed, the overall market mood was bleak after Wall Street stocks slid on Friday, with biotech and other "momentum" stocks again leading the Nasdaq sharply lower and weak results from JPMorgan dragging down banks.
Rising tensions in Ukraine also weighed on global investor sentiment. Ukraine has given pro-Russian separatists a Monday morning deadline to disarm or face a "full-scale anti-terrorist operation" by its armed forces, raising the risk of a military confrontation with Moscow.
Still, many market players were hopeful that Japanese shares' relatively cheap valuations and expectations of more easing by the Bank of Japan would eventually support the market.
"It seems like the notorious 'Sell in May (and go away)' season arrived early this year, suggesting that the summer rally may begin earlier than July," said Masatoshi Kikuchi, pan-Asian chief equity strategist at Mizuho Securities.
Other notable movers included Sharp Corp, which fell as much as 10% and hit a five-month low. The Asahi newspaper said Sharp, Japan's largest display maker, is considering another issue of new shares that could raise around 200 billion yen to replenish its depleted capital base.
The broader Topix gained 0.5% to 1,139.41 in thin trade, with trading volume at 30% of the full daily average for the past 90 days.
The JPX-Nikkei Index 400, a recently introduced gauge comprised of companies with a high return on equity and robust corporate governance, rose 0.4% to 10,368.85.