Japanese gaming giant Nintendo soared again Thursday, taking a week-long rally to 75 percent as investors ride the coattails of the Pokemon Go phenomenon sweeping the planet.

The scorching performance helped propel the broader Nikkei stock index almost one percent higher to break above the levels seen on June 23 before Britain's shock EU exit vote sent financial markets into turmoil.

Nintendo climbed 15.89 percent to 25,300 yen ($240) Thursday, compared with the 14,380 yen close last Wednesday as the new smartphone game launched.

Investors are betting its surprise popularity is a good sign for the console maker's nascent push into mobile gaming.

"The expectation is that Pokemon Go's success will contribute to the success of Nintendo's other original games, and even to the success of its next game console," SMBC Nikko Securities analyst Eiji Maeda told AFP.

But "the share price is reaching its upside limit".

The surge helped the broader markets rack up a fourth day of gains, with investors keenly awaiting details of a flagged government spending package aimed at boosting growth in the world's third-largest economy.

Speculation is rife Tokyo could unleash stimulus worth around 10 trillion yen after Prime Minister Shinzo Abe ordered a minister to prepare fiscal measures.

Investors are also eyeing a July 28-29 Bank of Japan meeting, which could see policymakers further ease monetary policy.

By the close, the Nikkei 225 was up 0.95 percent, or 154.46 points, at 16,385.89 -- putting it for the first time above the June 23 close of 16,238.35 before being hit by the Brexit shock.

The broader Topix index of all first-section shares tacked on 0.84 percent, or 10.90 points, to 1,311.16.

A rise in the dollar to 105.54 yen from 104.52 yen in New York also provided support.

Printing firms surged on reports Japan's Emperor Akihito wants to abdicate from the throne -- a development that would mean documents and commercial books using an imperial-era date system having to be updated.

Among the gainers, Mitsumura Printing soared 8.02 percent to 202 yen.

Toyota climbed 0.35 percent to 5,648 yen, Sony jumped 2.86 percent to 3,162 yen and factory robot maker Fanuc was 1.48 percent higher at 17,435 yen.

Uniqlo-operator Fast Retailing, a market heavyweight, slipped 1.72 percent to 27,660 yen before it released its latest earnings.

After markets closed, the company reported a 46 percent drop in net profit for the nine months to June.