A woman walks past an electronic screen displaying stock quotation board in Tokyo, Japan April 15, 2025. REUTERS/Issei Kato/ File Photo

By Kevin Buckland

TOKYO (Reuters) -Japan's Nikkei share average breached the 43,000-mark for the first time on Wednesday, with the broader Topix index also scaling a fresh all-time peak, tracking Wall Street's overnight gains and extending the rally to a sixth straight session.

The Nikkei gained as much as 1.7% to touch an unprecedented 43,451.46 before ending the day at a record-high closing level of 43,274.67.

That took its winning run to 7.4% since August 4. Monday of this week was a national holiday in Japan.

The broader Topix advanced as much as 1.2% to a record 3,103.31 points, before finishing at 3,091.91 - also booking a sixth-straight session of gains.

Overnight, the S&P 500 and Nasdaq ended at record highs as a moderate reading of July inflation bolstered bets for a Federal Reserve interest rate cut next month. [.N]

"A sense of relief is permeating through markets" following the U.S. Consumer Price Index (CPI) data, leading Japanese stocks "to take a step higher," said Maki Sawada, an equities strategist at Nomura Securities.

At the same time, "there are signs that the Nikkei is overheated after its extremely steep rally, and a steep drop at any time wouldn't come as any surprise," she added.

The Nikkei's relative strength index (RSI) rose above 75, well beyond the 70 line that many analysts consider indicative of an overheated market. The RSI was at a similar level on July 24, and the Nikkei fell in the following four sessions.

Of the Nikkei's 225 components, 151 rose versus 74 that fell.

Tech shares stood out, with chipmaker Renesas Electronics jumping almost 7%, chip-testing equipment maker Advantest rising 5.4% and Sony Group gaining 3.5%.

A strong earnings season continued to power big advances for some stocks, with tyre maker Yokohama Rubber vaulting 8.3% to be the Nikkei's biggest percentage gainer.

Athletic apparel company Asics soared nearly 18% after its favorable financial results to be the best-performing Topix stock.

(Reporting by Kevin Buckland; Editing by Sumana Nandy and Jamie Freed)