[Nikkei Recap] Sept 15, 2026: Nikkei 225 Almost Flat at 63,484 as SoftBank Group Jumps 7%+ in a Tug-of-War AI Trade

Hey everyone, Hirokichi here.

On September 15, 2026, the Nikkei 225 closed almost flat, down just 8.89 yen at 63,484.10. In the morning session, bargain-hunters bought back into AI and semiconductor names that had sold off sharply the day before, pushing the index up as much as 589 points at one point. But rising long-term interest rates weighed on the market through the afternoon, and the index gave back nearly all of that gain by the close. While the headline index barely moved, individual stocks told a very different story today. Let’s walk through what happened and, more importantly, why.

Today’s index moves

First, here’s how the major indexes closed.

What stands out here is that the Nikkei 225 was essentially flat while TOPIX fell a more meaningful 0.52%, and the Growth 250 Index actually finished in positive territory. Large-cap stocks with heavy weight in the Nikkei 225 moved sharply on stock-specific news, while rate-sensitive sectors like banks and real estate (which make up a big chunk of TOPIX) stayed under pressure. That’s the kind of “index divergence” day we saw today.

The Nikkei opened with buying and climbed as much as 589 points (+0.93%) from the prior close. On September 14, comments from AI industry leaders warning that AI investment might be moving too fast triggered heavy selling in AI and semiconductor stocks, and the Nikkei had finished that day down 518 points. On the 15th, the view spread that Monday’s drop had been overdone, and bargain-hunting buyers stepped back in.

That rally didn’t last, though. Japan’s 10-year government bond yield climbed to 3.030%, up 0.045 points from the previous day, and that weighed on stocks broadly through the afternoon, erasing the morning’s gains. The yen also weakened to the mid-154 range against the dollar, which would normally be a tailwind for exporters, but the drag from rising rates proved stronger.

What moved the market today

Here are the three main threads behind today’s action.

(1) A bounce-back from yesterday’s AI-stock selloff: On the 14th, comments from AI industry leaders suggesting AI investment was moving too fast triggered concentrated selling in AI and semiconductor names. Today’s morning rally was largely a bargain-hunting bounce from that overdone move.

(2) Rising domestic long-term interest rates: Japan’s 10-year JGB yield rose to 3.030%, up 0.045 points. Higher rates tend to be a headwind for equities broadly, and especially for real estate stocks and growth stocks whose value depends heavily on future earnings. This rate move essentially canceled out the morning’s gains.

(3) The prior day’s US market, currency, and oil moves: The Dow Jones closed down 152.09 points at 52,421.20 on September 14 (the previous trading day), a soft finish for US stocks. Meanwhile, the yen weakened into the mid-154 range against the dollar, and WTI crude oil rose to the 103-dollar range. Higher oil prices tend to feed inflation worries, which likely contributed to the rise in interest rates.

Stocks that made headlines today, and why

Now let’s look at the individual stocks that moved the most today. While the Nikkei 225 barely budged, individual names ranged from gains of over 16% to declines of nearly 3%.

This table shows that even within the same “AI and semiconductor” bucket, the buying wasn’t uniform — Lasertec rallied on bargain-hunting while Advantest moved the opposite way. That tells you today’s rebound wasn’t a blanket rally across the sector.

SoftBank Group (9984): up 7.54% to 6,279 yen

The biggest mover of the day was SoftBank Group. On the 14th, its stock had plunged on reports that its portfolio company OpenAI might delay its IPO, and that single stock alone dragged the Nikkei 225 down by 563 points. Today’s rally started as a bounce-back from that overdone selloff.

On top of that, there was a real piece of positive news on the financing side. SoftBank Group had a 25.9-billion-dollar credit line coming due on the 15th, but the company reportedly secured a new two-year, 11.87-billion-dollar credit facility from around 20 domestic and international banks — exceeding its original 10-billion-dollar target. That significantly eased concerns about refinancing risk, and the market welcomed the news. Combined with yesterday’s plunge, it made for a volatile couple of days, and it’s a reminder of just how closely the market watches this stock as a bellwether for AI-related sentiment.

Lasertec (6920): up 3.22% to 35,590 yen

Semiconductor equipment maker Lasertec rode the same wave as SoftBank Group. After yesterday’s selloff driven by AI-slowdown worries, this morning saw a view spread that those fears had been “excessive” and were cooling off, and bargain-hunters stepped in. Semiconductor names carry significant weight in the Nikkei 225, and they helped cushion the index today.

Advantest (6857): down 2.96% to 30,160 yen

On the other hand, not every semiconductor heavyweight joined the rebound. Advantest, a major semiconductor test equipment maker, moved against the trend even as peers like Lasertec rallied. We couldn’t find any specific negative news driving the move, so this is one figure we’re marking as “unconfirmed” for now. Market chatter points to profit-taking after the stock’s valuation had climbed quite high, along with a possible rotation out of high-P/E (price-to-earnings ratio, a measure of how many times a stock’s price is trading relative to its earnings) names amid rising long-term rates.

Sumitomo Mitsui Financial Group (8316): down 2.67% to 6,842 yen

A representative bank stock, Sumitomo Mitsui Financial Group, also declined. Rising long-term rates typically benefit bank profitability through higher lending margins, so this would normally be a tailwind. But on the 14th, market commentary had already flagged that the “buy banks on rate hikes” trade had pushed bank-stock gains to AI-stock-like levels, and that further rate increases might already be priced in. Today’s decline looks like a continuation of that unwind. Other rate-sensitive names, including Resona Holdings and Mitsubishi Estate, also showed up among the day’s biggest decliners, suggesting a broader pullback across financials and real estate.

What this means for individual investors

On a day like today, when the headline index barely moves but individual stocks swing anywhere from +16% to -3%, it’s easy for less experienced investors to feel lost about what’s actually happening. Personally, I think days like this are exactly when it’s important not to get too caught up in the “average” number and forget to look underneath it.

If you’re dollar-cost averaging into index funds, today’s swings honestly don’t change much for you. The index itself closed essentially flat, so just keep contributing as usual.

If you hold individual stocks, or you’re looking to trade shorter-term moves, today was a good reminder not to lump everything together as “AI and semiconductor stocks.” It pays to check the specific reason behind each stock’s move one by one — as we saw, Lasertec and Advantest reacted in opposite directions even though they’re in the same sector.

What to watch going forward

Here are three things worth keeping an eye on.

(1) The path of long-term interest rates: Since rising rates were the main reason today’s morning gains were erased, how far the 10-year JGB yield climbs above 3%, or whether it stabilizes, will likely keep driving moves in financials, real estate, and growth stocks.

(2) AI-related names like SoftBank Group: Given the sharp swings over the past two days (a plunge followed by a rebound), it’s worth watching whether that volatility continues, and whether more stocks like Advantest start moving against the broader AI-sector trend.

(3) The yen and the US market: The dollar has weakened into the high-154 range against the yen, and whether that level holds will matter for export-related earnings expectations. With the Dow’s soft finish on the 14th, tonight’s reaction in the US market is also worth watching.

Let’s keep at it, slow and steady. See you tomorrow!

* This article is for informational purposes only and does not recommend any specific investment. Please make investment decisions at your own responsibility.

(Sources: Nikkei, Zaikei Shimbun/Fisco, Investing.com)

Previous trading day’s recap →Sep 14, 2026 recap

日本語版はこちら →Japanese version

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