Monday was two markets wearing one flag. The Nikkei 225 closed down 0.81% at 63,492.99, dragged by a violent unwind in the AI complex, while the broader TOPIX — tracked here via the 1306 ETF proxy — rose 0.86% to 423.30. The trigger was external: weekend remarks from OpenAI CEO Sam Altman and Anthropic CEO Dario Amodei advocating a slowdown in advanced AI development on safety grounds, compounded by reports that OpenAI will not pursue an IPO in 2026. The single biggest casualty was SoftBank Group (9984), which collapsed 10.72% to 5,839 on 1.3x its 20-day volume — a mega-cap drawdown that sat squarely at the center of the day’s index divergence. The yen was a non-event: USD/JPY closed at 154.53, essentially flat on the day.
The AI Complex vs. Everything Else
Within our fixed 95-name large-cap universe (not a full-market scan), the losers were concentrated exactly where you would expect: SoftBank -10.72%, Murata (6981) -2.52%, Advantest (6857) -2.02% to 31,080, Tokyo Electron (8035) -1.03% to 50,930, with SCREEN (7735) off 1.22%. Notably, volume on the chip names was unremarkable — Advantest traded at 0.9x its 20-day average — suggesting orderly de-rating rather than capitulation.
The other side of the tape was strong. Fujitsu (6702) jumped 7.39% on 1.9x average volume — the day’s standout by both price and participation — with NEC (6701) +6.90% and Recruit (6098) +6.35% close behind. Sony (6758) gained 4.30% to 3,788, and Bandai Namco (7832) added 4.81%. Among the bellwethers, MUFG (8306) rose 1.61% to 3,720, Fast Retailing (9983) added 0.42%, and Toyota (7203) slipped a modest 0.20% to 3,025.
Sectors: 14 of 17 Advanced
Using TOPIX-17 ETF proxies (Nomura NEXT FUNDS closes, which can deviate slightly from official sector indices), breadth was firmly positive despite the headline Nikkei decline:
| Sector | Day | vs TOPIX | 5-day |
|---|---|---|---|
| Financials ex-Banks | +2.55% | +1.70pp | +1.7% |
| Transport & Logistics | +1.87% | +1.01pp | +1.3% |
| Banks | +1.66% | +0.80pp | +0.5% |
| Energy Resources | +0.00% | -0.86pp | +4.4% |
| Electric & Precision | -0.08% | -0.94pp | -5.3% |
| Steel & Nonferrous | -2.06% | -2.91pp | -5.0% |
Financials leading into a Bank of Japan meeting week is a coherent story, and the 5-day figures show Electric & Precision already down 5.3% before today — the AI de-rating has been a week-long process, not a one-day event. Energy Resources sat flat today but remains up 4.4% over five sessions, consistent with the crude-supply headlines out of Saudi Arabia that dominated the commodity tape.
Positioning: The Selling Was Not Defensive
Our daily signature indicator: TSE short sales were 38.1% of total trading value on Monday (31.4% price-rule restricted plus 6.7% unrestricted), on total turnover of JPY 8.03 trillion. That is the lower third of the last eight sessions’ 38.1%–44.9% range, versus a 41.9% average — meaning short selling was comparatively subdued and today’s decline was not driven by an aggressive defensive shorting wave, though the aggregate ratio cannot tell us who was selling or what they held.
The Nikkei Volatility Index told a more nervous story, rising 1.26 points to 31.06 — the 85th percentile of the last 905 sessions, firmly elevated.
Friday’s JSF standardized margin data (September 11 — the latest available, so it predates today’s plunge) is worth flagging on SoftBank specifically: loans for margin buying rose 270,400 shares to 2.82 million while stock lending — shares borrowed for shorting — actually fell 19,000 shares. In other words, leveraged retail longs were adding into Friday and short-side borrow was shrinking, right before a double-digit drawdown. Tuesday’s update will show how much of that long position survived. Elsewhere in the same dataset, Advantest and Tokyo Electron both saw margin-buying balances rise (+84,000 and +107,900 shares respectively) — dip-buying demand into the chip weakness.
Squeeze costs remain broad: 411 of 871 loanable issues carried a gyaku-hibu premium charge as of Friday, led by the WTI Crude Oil ETF (1671) at roughly 98.6bp per day of price — and JSF hit that same ETF with a new-application suspension and a maximum-rate multiplier notice today, a direct echo of the crude squeeze. On the regulatory side, JPX published 1,006 large disclosed short-position filings across 664 issues today; these are lagged position disclosures, not today’s flow — SHIFT (3697) at 10.4% aggregate and OSAKA Titanium (5726) at 9.4% remain the notable crowded names.
Rates: JGBs Backing Up Into the BOJ
The latest MOF official yields (Friday, September 11) showed a bear-steepening move: the 10-year at 2.987% (+6.7bp on the day), the 5-year at 2.296% (+5.2bp), and the 30-year above 4% at 4.024%. A 10-year knocking on 3% four days before a policy meeting is doing a lot of the work behind the banks’ outperformance.
Weekly Flows
The latest JPX investor-type data covers the week of August 31–September 4 — these are weekly figures published with a lag, not today’s flows. On TSE Prime, foreign investors were net sellers of JPY 0.17 trillion and individuals net sellers of JPY 0.05 trillion. A caveat: MOF’s independent cross-border series for roughly the same week (Aug 30–Sep 5, different reporting basis) showed foreigners as net buyers of JPY 0.69 trillion of Japanese equities. When the two series disagree, we treat foreign direction as genuinely ambiguous rather than picking a side. Separately, JPX weekly margin balances (Tokyo+Nagoya, as of September 4) showed margin buying at JPY 6.48 trillion against margin selling of JPY 0.85 trillion — retail leverage still heavily long-tilted.
What to Watch
- BOJ policy decision, September 17–18. With the 10-year JGB near 3% and financials leading the tape, the meeting is the week’s central event.
- The overnight US setup. S&P 500 futures were marked at 7,608.50 (-0.67%) during Tokyo hours versus Friday’s 7,656.98 cash close — the AI de-rating is a global trade, and Tuesday’s open inherits whatever New York does with it.
- Tuesday’s JSF margin update on SoftBank. Friday showed leveraged longs adding and short borrow shrinking just before a 10.7% drawdown; the next print reveals whether that positioning was forced out.
Disclaimer: This is an information and analysis publication, not investment advice. See our Methodology for data sources, standards, and our corrections policy.