[This Week’s Stock Market] Nikkei 225 up 1945 yen, TOPIX falls. A week led by semiconductors｜ゆげまる

Writing this on Saturday, October 3, 2026.

🐻 Fundamental Bear’s Weekly Stock Market Commentary

🐻 “First, let’s look back at this week’s numbers.”

・The Nikkei 225 rose 1945 yen for the week, climbing from 66,364 yen to 68,309 yen.

・Meanwhile, the TOPIX fell 0.91% for the week.

・The Nikkei 225 had 3 days of losses and 2 days of gains.

・On the 29th, the end-of-September dividend ex-rights date acted as a downward pressure on stock prices.

・On the 30th, all 33 industry sectors rose.

・On the 1st, the Nikkei 225 rose 2203 yen following Micron’s strong earnings report.

・On the 2nd, profit-taking selling became dominant, and the market closed down 647 yen.

🐣 “The Nikkei 225 went up by 1945 yen, but the TOPIX went down?”

🐻 “That’s right.

This week, there were movements that you couldn’t see just by looking at the Nikkei 225 figures.”

📅 This week’s market movements

First, let’s look back starting from Monday.

September 28 (Mon): Down 486 yen

The Nikkei 225 fell for the first time in 6 days.

In addition to the reaction from the continued gains until the previous week, caution regarding U.S. long-term interest rates and the situation in the Middle East weighed on the market.

September 29 (Tue): Down 396 yen

This day was the ex-dividend date for the end of September.

There was an impact from the “dividend drop,” where stock prices fall because the right to receive dividends is lost.

The impact on the Nikkei 225 is estimated to be in the high 300-yen range.

However, since actual stock prices are also affected by trading other than the dividend drop, not all of the decline can be explained by the dividend drop alone.

The TOPIX also fell 1.72%.

September 30 (Wed): Up 1272 yen

The trend changed here.

The Nikkei 225 rebounded significantly, and all 33 industry sectors rose.

It was a day where not only semiconductor-related stocks but a wide range of stocks were bought.

October 1 (Thu): Up 2203 yen

This was the day with the largest gain this week.

Following Micron’s strong earnings, semiconductor-related stocks surged.

The Nikkei 225 rose 3.30%, coming within 5 yen of 69,000 yen.

However, the TOPIX’s gain was limited to 0.57%.

October 2 (Fri): Down 647 yen

Since it had risen more than 3400 yen in the previous two days, profit-taking selling became dominant.

The high level of U.S. long-term interest rates and the Middle East situation continue to be factors for caution.

🐣 “It’s a busy week with ups and downs.”

🐻 “Moreover, the sectors that rose differed depending on the day.

That’s the interesting part about this week.”

💾 The big news this week was Micron’s earnings

In this week’s market, the earnings of U.S. memory semiconductor giant Micron were particularly noteworthy.

They were announced after the U.S. market closed on September 30, and the details were reported on the morning of October 1, Japan time.

The full-year earnings for fiscal year 2026 were as follows:

・Revenue was approximately $133.2 billion, about 3.6 times the previous period.

・Operating profit was approximately $99.3 billion, about 10 times the previous period.

・Operating profit margin rose from 26.1% to 74.6%.

🐣 “Operating profit being 10 times higher is amazing!”

🐻 “That’s not all. The future outlook was also strong.”

The revenue forecast for the next quarter provided by Micron was $61.5 billion at the midpoint.

This exceeded market expectations.

Furthermore, the company also indicated a forecast that the supply and demand for memory will become even tighter from fiscal year 2027 to 2028.

🐣 “So they think there will be a memory shortage not just now, but in the future as well.”

🐻 “That’s right.

However, since it is just the company’s outlook, it doesn’t necessarily mean it will go as expected.”

Following the strong results and outlook, semiconductor-related stocks such as Advantest and Tokyo Electron rose significantly in the Tokyo market on October 1.

This became a major factor supporting the 2203 yen rise in the Nikkei 225.

🔀 Nikkei 225 rose. But TOPIX fell

This week, what I was particularly concerned about was this difference.

The Nikkei 225 rose 2.93% for the week.

Meanwhile, the TOPIX fell 0.91%.

🐣 “Even though they are both Japanese stock indices, why do they move in opposite directions?”

🐻 “It’s because the calculation methods for the indices are different.”

The Nikkei 225 is an index calculated based on the stock prices of 225 companies.

Therefore, it has the characteristic that the price movements of high-priced stocks tend to have a large impact on the index.

On the other hand, the TOPIX is calculated based on the market capitalization of free-float shares.

It is an index that reflects the movements of a wider range of stocks than the Nikkei 225.

This week, semiconductor-related stocks, which have a large impact on the Nikkei 225, rose, while selling occurred in a wide range of other stocks, creating a difference between the two indices.

The gap was particularly wide on October 1.

The Nikkei 225 was up 3.30%.

The TOPIX was up 0.57%.

🐣 “That’s nearly a 6-fold difference!”

🐻 “It means that stocks with a large impact on the Nikkei 225 were bought in particular.”

In fact, on the Tokyo Stock Exchange Prime Market that day, there were 750 stocks that rose and 747 that fell.

It was almost half and half.

Just because the Nikkei 225 rose by 2,203 yen does not mean that all stocks rose significantly.

🐻 “If you only look at the Nikkei 225, you might feel like the entire market is rising.

That’s why I also want to check the TOPIX and the number of stocks that rose and fell.”

🔁 The sectors being bought changed from day to day

This week, there were also differences in the movements of each sector.

On the 29th, due in part to the impact of dividend ex-dates, a wide range of stocks, including financial stocks, fell.

On the 30th, all 33 sectors rose.

However, on the 1st, while semiconductor-related stocks pushed the Nikkei 225 up significantly, 22 sectors, including banks and insurance, fell.

On the 2nd, 29 out of 33 sectors fell.

🐣 “Everything went up on the 30th, but almost everything went down on the 2nd, didn’t it?”

🐻 “That’s right.

Even in the same week, the same stocks weren’t being bought every day.”

Not just whether the Nikkei 225 went up or down, but which sectors moved.

If you look that far, this week’s market looks a little different.

📊 The Tankan survey was also released

This week, the Bank of Japan’s Tankan survey was also released on October 1st.

🐣 “What was the Tankan again?”

🐻 “It’s a survey where the Bank of Japan asks companies about the state of the economy.”

The official name is the ‘Short-Term Economic Survey of Enterprises in Japan’.

It is published once every three months.

One of the figures that attracts attention is the Business Conditions DI.

It is calculated by subtracting the percentage of companies that answered ‘bad’ from the percentage of companies that answered ‘business is good’.

In this survey, the Business Conditions DI for all sizes and all industries improved from the previous plus 18 to plus 21.

Large manufacturing companies also improved from plus 22 to plus 24.

On the other hand, large non-manufacturing companies worsened from plus 37 to plus 35.

🐣 “It got better overall, but there are differences depending on the industry, aren’t there?”

🐻 “That’s right.

Not just stock prices, but how companies actually feel about the economy is also material for looking at the market.”

🐣 Chick’s Question of the Day | If the Nikkei 225 is rising, isn’t the economy good too?

🐣 “The Nikkei 225 rose by 1,945 yen this week, didn’t it?
Does that mean the Japanese economy is also doing very well?”

🐻 “That’s not necessarily the case.”

Stock prices are not determined solely by a company’s current performance.

Expectations that profits will increase in the future, interest rates, exchange rates, and the movements of overseas markets also have an impact.

Furthermore, when some stocks rise significantly like they did this week, the TOPIX can fall even if the Nikkei 225 is up significantly.

🐣 “I see. Stock prices and the economy are not the same thing, are they?”

🐻 “That’s right.

That’s why I want to look at corporate performance and economic indicators along with stock prices.”

👀 Things to watch next week

There are a few things to keep an eye on next week as well.

First is US long-term interest rates.

If interest rates remain high, it could affect the valuation of stocks.

Next is the situation in the Middle East and crude oil prices.

If high crude oil prices persist, it will be a factor that pushes up corporate costs and prices.

And finally, semiconductor-related stocks.

Will the buying triggered by Micron’s strong earnings continue, or will there be profit-taking sales?

As these stocks have a large impact on the Nikkei 225, I want to continue to pay attention to them.

🐻 “Let’s look not only at the Nikkei 225 figures, but also at the movements of the TOPIX and individual sectors.”

♨️ Yugemaru’s Summary

The Nikkei 225 rose 1945 yen this week. Looking only at the numbers, it was a week of significant gains. However, looking at the details, it rose for two days and fell for three. Moreover, the TOPIX fell 0.91% for the week. What left the biggest impression on me was, of course, the difference between the Nikkei 225 and the TOPIX on October 1st. The Nikkei 225 was up 3.30%, while the TOPIX was up 0.57%. Even though they are both Japanese stocks on the same day, they are so different. If I had only looked at the Nikkei 225, I would have just thought, ‘It went up a lot today!’ But in reality, the number of advancing and declining stocks was about half and half. And Micron’s earnings were also intense. In addition to the fact that operating profit was about 10 times that of the previous period, there is a forecast that the supply and demand for memory will become even tighter through fiscal year 2028. Of course, it is not guaranteed that things will go as the company expects, but I am also curious about the future earnings of semiconductor-related companies. Next week, I would like to continue looking not only at the Nikkei 225 figures, but also at the content of the market. Everyone, thank you for your hard work this week as well. 🙏 * This note is a place to enjoy investing as entertainment, so there is no intention to recommend specific stocks. However, for the sake of format, characters may sometimes make assertive statements. Please understand that those are the opinions of the characters and not my recommendations. * This article was written on October 3, 2026.