TOKYO, June 30 (Reuters) - Japanese stocks erased early gains to trade flat on Wednesday, as investors held back from making big bets on concerns of the Delta variant of COVID-19 in Asia and amid a nine-month-old trend of a weak finish on the last trading of the month.

At midday, the Nikkei average was flat at 28,815.10, having erased early gains of 0.65%. The broader Topix edged up 0.03% at 1,949.97.

Shares initially took cues from an overnight rally in Wall Street, but investor-buying quickly succumbed to anxiety about the Japanese markets' peculiar pattern since September to fall on the last trade of the month.

Some market players think it could be due to month-end rebalancing by big investors, while others think it is just a coincidence.

"It's just an anomaly. But then again, a lot of people are talking about it, so it does have some effect on the psychology," Masato Kogure, group leader of trade execution at Tokai Tokyo Securities said.

The market flitted within a range, underperforming global shares as investors weigh the progress in vaccination rollout against a surge in domestic infections ahead of the Olympics next month.

Among big movers, Sugi Holding tumbled 7.8% after the drugstore chain operator's quarterly earnings fell short of market expectations.

Nitto Boseki slid 6.1% after one of its shareholders announced a plan to sell almost 1 million shares, or about 2% of the outstanding, of the textile company.

Shares of J. Front Retailing dropped 3.8% after the department store operator cut its profit outlook.

Chugai Pharmaceutical rose as much as 7.9% after it applied for regulatory approval in Japan of an antibody treatment for COVID-19.

Murata Manufacturing gained 3.1% after the company said it sees merit in lowering the minimum volume investors are able to trade in its shares while Ushio Inc jumped 12.7% after the lamp maker lifted its earnings outlook, doubling its net profit forecast for the current year through March. (Reporting by Hideyuki Sano; editing by Sherry Jacob-Phillips)