TOKYO, May 22 (Reuters) - Japan's Nikkei share average ended higher on Monday, posting an eighth straight session of gains, as investors continued to scoop up discounted domestic stocks amid optimism for corporate efforts to boost returns to investors.

The Nikkei reversed course to jump 0.9% to 31,086.82, its highest close since July 1990 and in the longest winning streak since April 2023.

The broader Topix rose 0.66% to 2,175.90.

The Nikkei hit its 33-year high on Friday, buoyed by ongoing improvement of shareholder returns, robust outlook and the yen's weakness.

"The Nikkei's gain accelerated in the afternoon session probably because overseas investors tried to buy more Japanese stocks," said Chihiro Ohta, assistant general manager at the investment research and investor services at SMBC Nikko Securities.

"But the market might have peaked and may pause its gains in a short term partly because on jitters surrounding U.S. debt ceiling negotiations."

Non-life insurers led the gains after Tokio Marine Holdings Inc and its peers posted robust outlook after market close on Friday. Tokio Marine, which also announced a buyback of up to 1.5% of its own shares, surged 5.72% on Monday.

Shares of MS&AD Insurance Inc advanced 1.68% but Sompo Holdings Inc cut its gains, falling 0.22%.

The insurance sector jumped 2.35% to become the top gainer among the Tokyo Stock Exchange's 33 industry sub-indexes.

The airlines and railways sub-indexes rose 2.21% and 1.62%, respectively.

Drug maker Daiichi Sankyo Co Ltd fell 1.93% to become the biggest loser on the Nikkei, while chipmaker Renesas Electronics Corp lost 1.93%.

Shigetoshi Kamada, general manager at the research department at Tachibana Securities, said the market rally, which was led by foreign investors, could continue as retail investors are seen joining the buying spree.

"It seems the trend of share buybacks will never end," he said.

(Reporting by Junko Fujita; Editing by Sherry Jacob-Phillips and Varun H K)