The short answer
Say you had a time machine and put 600,000 yen into Kioxia. How much would it be worth now?
Assume you bought actual shares at the IPO price of 1,455 yen and held them until the closing price of 65,850 yen on May 29, 2026. Here's what you'd get.
Japanese stocks are normally traded in lots of 100 shares, so 600,000 yen buys you 400 shares.
IPO price: 1,455 yen
Shares bought: 400
Purchase cost: 1,455 yen × 400 shares = 582,000 yen
Leftover cash: 18,000 yen
Closing price on May 29, 2026: 65,850 yen
Value of the shares: 65,850 yen × 400 shares = 26,340,000 yen
Including leftover cash: 26,358,000 yen
So roughly 600,000 yen would have become roughly 26.36 million yen.
That's huge.
But the idea that "600,000 yen turned into 100 million" doesn't hold up if you're buying ordinary shares.
Even if we assume you could buy exactly 600,000 yen's worth through fractional shares (Japan's odd-lot trading, where you can buy fewer than 100 shares),
600,000 yen ÷ 1,455 yen × 65,850 yen
= about 27,154,639 yen
that's roughly 600,000 yen becoming roughly 27.15 million yen.
Still nowhere near 100 million.
What about after tax?
Once you factor in tax, the 400-share case looks like this.
Purchase cost: 582,000 yen
Sale value: 26,340,000 yen
Profit: 25,758,000 yen
Tax rate: 20.315%
Tax: about 5,231,748 yen
Estimated after-tax total, including leftover cash: about 21,126,252 yen
In other words, if you sold and paid the tax, you'd end up with about 21.12 million yen.
That's still impressive.
But again, it's not 100 million.
You couldn't have bought it "two years ago" anyway
The first thing to know is that Kioxia wasn't even listed in 2023 or the first half of 2024.
Kioxia Holdings listed on the Tokyo Stock Exchange on December 18, 2024.
The IPO price was 1,455 yen, and the first trade of the day was at 1,440 yen.
So in September 2023 or early 2024, an ordinary individual investor simply couldn't have bought Kioxia shares.
That's why, when you see a social media post saying "if you'd put 600,000 yen in two years ago, you'd have 100 million," your first move should be to question the premise.
If a claim like that were true, it would have to rest on something else, such as:
- It's talking about unlisted shares or some special kind of investment
- It mixes in margin trading or other leverage
- It's confusing a different stock or a different time period
- The share count or share price is wrong
- It's just exaggerated
At the very least, "bought two years ago and turned it into 100 million" doesn't work as ordinary stock investing.
Remembering Kioxia was a pretty sharp observation
Still, I think the fact that Kioxia stuck in your memory is a good sign.
Kioxia is the company that grew out of Toshiba's memory business. It's a Japanese chipmaker that makes flash memory and SSDs.
When you read a book about semiconductors, a few things stood out: Yokkaichi (where Kioxia's main fab is), memory, a Japanese company, and Kioxia.
That's a keen eye for how an industry fits together.
Thinking "hey, this company matters" is worth something, both as an investor and as someone who writes about this stuff.
A strong company and a stock worth buying are two different things
The key point is that a company being strong and its stock being a good buy are separate questions.
Kioxia is an important company.
But to buy its shares at the IPO, you'd have had to answer questions like these:
- What price counts as cheap?
- What price counts as expensive?
- How long will you hold?
- Where will you sell?
- What will you do if it falls?
- What's the most you're willing to lose?
- How will you read the memory chip market cycle?
- Will you keep holding through earnings reports?
- Are you holding it as a hot-theme stock?
- What will you do if it turns into a bubble?
If you haven't settled those, you're just investing on vibes.
"It's famous, so I'll buy it." "It looks strong, so I'll buy it." "I read about it in a book, so I'll buy it." "It seems like the only one in Japan, so I'll buy it."
Sometimes that works out.
But it's hard to repeat.
Huge single-stock wins you can't backtest may not be your game
Different investing styles suit different people.
If you like to look at things through backtests (testing a strategy on past data), drawdowns (how far your account falls from its peak), the odds of going bust, standard deviation (how wildly prices swing), Monte Carlo simulations (running thousands of random scenarios), and rule-based trading, a windfall like this is hard to work with.
The reason is that it's hard to see anything repeatable in it.
Of course, there are ways to build repeatability into stock picking too:
- Fundamental analysis (looking at a company's real earnings and finances)
- Theme analysis
- Supply and demand analysis
- Earnings analysis
- Valuation analysis (judging whether the price is fair)
- Industry cycle analysis
- Portfolio management
- Stop-loss rules (selling automatically once a loss reaches a set limit)
- Holding-period rules
But "I thought that company was great, so I should've bought it" is something anyone can say after the fact.
Back then, it could just as easily have gone down.
Right after the listing, the first trade was actually below the IPO price.
Around the IPO, the listing plan had also been postponed and reworked because of investor skepticism about its valuation and a downturn in the chip market.
In other words, it carried plenty of real risk at the time.
Time-machine investing breeds regret
"What if I'd bought back then?" is the most enjoyable and the most dangerous game in investing.
With a time machine, anyone can win.
If you only look back at the stocks that went up, you can make yourself a genius every time.
In reality, there's no time machine.
Back then, you were in a situation like this:
- You didn't know if it would really go up
- You didn't know how far it might fall
- You didn't know when to sell
- You didn't know if you could stomach a crash along the way
- There were plenty of other stocks to consider
- You had to decide where to put your money
So it's wrong to think "I knew about it and didn't buy, so I'm a failure."
Here's how I'd put it instead.
You had the ability to read how an industry fits together. But you didn't have an investing rule for buying that stock. So you didn't buy. For your own investing operating system, that was working as intended.
Even if 600,000 yen became about 26 million, could you repeat it?
600,000 yen turning into about 26 million yen.
That's a nice dream.
But what matters for an investment decision is whether you can repeat the result.
Could you buy the next stock like this when you find it?
After buying, could you keep holding through a drop?
When it goes up, where do you sell?
At 5 times your money?
At 10 times?
At 20 times?
Could you hold all the way to 40 times?
If you haven't decided that far, then even if you happen to get lucky once, repeating it next time is hard.
A giant single-stock win looks easy when you only see the result.
In reality, you need all of these:
- The nerve to buy
- The strength to sit through declines
- The guts not to sell
- An understanding of the company
- An understanding of the market cycle
- Money management
- A call on when to take profits
What to take away from this
The lesson here isn't "next time, go all in on a stock like Kioxia."
It's more like the following.
1. You can spot important companies within an industry
You read a book on semiconductors and Kioxia stayed firmly in your mind.
That's a good observation.
You have a feel for which companies matter and which industries are likely to grow.
2. But without a buying rule, you can't get in
Knowing a company isn't enough to buy it.
To buy the stock, you need to decide:
- What price you'd buy at
- How far it can fall before you get out
- How much of your money goes into it
- How long you'll hold
- Under what conditions you'll sell
3. You don't have to make unrepeatable windfalls your main game
If you value backtests and rule-based investing, you don't have to make chasing single-stock bubbles your main focus.
Just win with the kind of investing that suits you.
4. If you really want to do it, keep it small in a satellite slot
If you want to try theme stocks tied to an industry, the realistic way is a small "satellite" slice (a small side portion kept apart from your core holdings) rather than your main assets.
For example:
- Just a few percent of your total assets
- Decide the maximum loss first
- Write down why you're buying
- Write down why you'd sell
- Review it at every earnings report
- Keep it to an amount where a failure won't affect your daily life
That way you can use your eye for industries while avoiding a devastating loss.
Wrap-up: With a time machine you'd win, but in real life you need rules
If you'd put 600,000 yen into Kioxia, it would have been worth about 26.36 million yen as of May 29, 2026.
Assuming you could buy exactly 600,000 yen's worth through fractional shares, it would be about 27.15 million yen.
That's impressive.
But with actual shares, it's not 100 million.
And in 2023 or the first half of 2024, you couldn't have bought it as an ordinary listed stock anyway.
So the claim that "600,000 yen two years ago would be 100 million now" is highly questionable, at least as a story about ordinary stock investing.
What matters more is this way of looking at it:
Remembering Kioxia was a sharp move. But not buying it makes sense given your investing rules. Knowing a strong company and buying its stock are two different things. There's no need to beat yourself up over time-machine investing. What you should take away isn't regret, but lessons you can fold into your own investing rules.
What counts in investing isn't regretting a one-off hit from the past.
It's how you'll handle the next similar moment under your own rules.
