October 2026 in Review: From Nikkei Euphoria to the AI Reckoning

Market Snapshot

Japan’s October stock market moved from an exuberant first week to a wary finish. The Nikkei 225 ended September 30 at 66,753.72 and October 30 at 63,290.11, a 5.19% monthly decline. TOPIX fell from 4,108.65 to 3,965.07, or 3.49%. These are comparisons of final cash-market price-index closes, not total returns.

The Nikkei reached an intraday October high of 70,798.62 on October 6 before touching 62,189.65 on October 26. That wide range captures the month better than either its opening optimism or final selloff alone. Tokyo cash equities did not trade on October 31 or November 1.

What Moved Tokyo

The defining tension was between confidence in global spending on artificial intelligence and concern about how rapidly that investment would generate earnings. Japanese semiconductor equipment and testing suppliers sit directly in that global spending chain. Their shares became a prominent vehicle for both enthusiasm and doubt.

Exchange rates, interest-rate expectations, corporate earnings and the domestic consumer outlook added other forces. This was not a month with one sufficient explanation for every trading session.

Today’s Market Mover

The theme of the month was AI-linked semiconductor equipment and testing, including Advantest (6857) and Tokyo Electron (8035). On October 30 the Nikkei plunged 1,369.36 points, or 2.12%, as chip and AI-related shares came under pressure.

This is a sector theme rather than a claim that one stock alone caused the monthly decline. We have not established comparable full-month returns for every constituent, so this report does not rank individual stocks by contribution. Confidence: Medium—strong evidence for the theme, but no full constituent attribution calculation.

Sector Pulse

AI-related technology swung sharply. Banks faced questions about how Japan’s rate normalization would affect margins, while exporters watched the currency and consumer-facing businesses navigated real-income pressures. The smaller October decline in TOPIX than in the Nikkei is an invitation to inspect index construction rather than a blanket verdict on domestic demand.

The Nikkei is price-weighted; TOPIX is based on free-float-adjusted market capitalization. Their different sensitivities to large technology names matter in a volatile month.

Yen Watch

A supplied reference quote put USD/JPY at 157.53 at 19:53 UTC on October 31—04:53 JST on November 1. It is a dated reference quote, not an official Tokyo month-end fixing or a month-average rate.

A weak yen can help exporters translate overseas revenue but raise the cost of imported fuel and food. No monthly percentage movement is stated because a fully consistent pair of beginning- and end-month FX observations has not been verified.

Rates / JGB Watch

The Bank of Japan held its overnight policy rate around 1.25% on October 30 after its September move. Investors remained focused on whether wage and price dynamics justify further normalization.

A consistently sourced, final October 30 ten-year Japanese government bond yield was not established for this report, so the snapshot leaves that figure blank rather than substituting a mismatched quote.

Global Handoff

Japan’s chip suppliers are entangled with the global AI investment cycle, so U.S. technology valuations, Treasury yields and the dollar were central cross-border influences. European and American sessions can change the tone before Tokyo reopens even when Tokyo itself is closed.

This is a retrospective monthly special with a next-open setup, not a fictional October 31 or November 1 trading-session summary.

Policy / BOJ Watch

The BOJ’s October outlook focused on the durability of underlying inflation near its 2% objective. Its rate hold did not settle the timing of the next adjustment; wages, imported costs, consumer spending and overseas risks remain relevant.

The central bank’s ETF sales and bond holdings are separate policy transmission issues. They should not be treated as evidence of a predetermined decision at the next meeting.

Publisher’s Market Note

October offered a reminder that a promising technology and an attractively priced stock are not the same thing. Japan’s role in supplying precision equipment for the AI era is real. Yet the market can still reassess how much future success it has already priced in. The distance between those two ideas was October’s story.

Before the Next Open

The next Tokyo cash session is Monday, November 2. Japan’s Culture Day holiday closes the exchange on Tuesday, November 3. Watch the yen, overseas semiconductor shares, domestic earnings, bond yields and any new BOJ or government commentary before the holiday interruption.

Sources and Method

Based on publicly available index, exchange and central-bank information, not reproduced subscription articles. Monthly price-index changes compare September 30 and October 30 closes. Unverified figures are omitted. This is not investment advice.

1. Nikkei Indexes — monthly historical prices
2. Japan Exchange Group — official TOPIX values
3. Bank of Japan — policy and outlook
4. QUICK October investor survey
5. Japan Market Desk previous week in review

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