ビットコインって使えるの？ 投資対象じゃないの？ #249
Most people who hold Bitcoin have never actually used it to pay for anything. This episode of Yuru Computer Science Radio (ゆるコンピュータ科学ラジオ) digs into why—covering the collapse in transaction fees, how the Lightning Network works, and what stablecoins can and cannot replace—before guest Kato-san from Nihon Bitcoin Sangyo K.K. (日本ビットコイン産業株式会社) reframes the entire debate as a question of ideology rather than technology.
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What this episode answers
Why has Bitcoin failed to catch on as a payment method for so many years?
The two main culprits are price volatility and high transaction fees. Volatility hits recipients hardest—¥1,000 received today could be worth ¥500 tomorrow—and in B2B deals with 90-day payment cycles the price swing can push a transaction into a loss. On fees, one host recalled paying ¥2,000 in fees just to send ¥1,000 to a friend in 2018.
How was the fee problem—once ¥2,000 to send ¥1,000—actually solved?
Two changes drove the drop: more efficient packing of transactions into each block (eliminating wasted space, like removing excess packaging), and the introduction of the Lightning Network. Today, sending ¥10,000 costs roughly ¥10 in fees—far cheaper than a bank international wire at around ¥3,000.
How does the Lightning Network work, and how does it prevent fraud?
Lightning keeps a private ledger between two parties and batches many transactions together, only writing the final balance to the blockchain—likened to settling a full day of mahjong scores at once rather than after every hand. Fraud is deterred because every payment message embeds information that would let the other party seize all of the cheater's funds if an old state is ever submitted to the chain, a mutual-assured-destruction structure that keeps the system honest without any administrator.
If stablecoins exist, is Bitcoin as a payment rail unnecessary?
Guest Kato-san pushes back: thinking in yen or dollars and treating stablecoins as the answer is itself the assumption Bitcoin supporters reject. From a Bitcoin-native worldview, stablecoins are not a substitute.
Why don't Bitcoin supporters treat its price volatility as a fatal flaw?
Kato-san's answer is that sharp volatility is not unique to Bitcoin—currencies like the South African rand fluctuate as much or more. Beyond that, he argues fiat stability is an artifact of enormous central-bank effort, and governments have a structural incentive to inflate away their debt, making fiat fundamentally less trustworthy in his view.
Two Reasons Bitcoin Is Not Used for Payments
Bitcoin ownership is widespread, but almost no one actually pays with it. The episode identifies two structural reasons: price volatility and transaction fees.
Volatility is primarily a problem for the recipient. Accepting ¥1,000 worth of Bitcoin today could mean holding ¥500 by tomorrow. The risk compounds in B2B commerce, where payment terms of 90 days are common; a dramatic price move in that window can turn a profitable deal into a loss.
On fees, one of the hosts shared a vivid personal memory from the 2018 crypto boom: he tried to send ¥1,000 to a friend and was quoted a ¥2,000 fee. When he went to complain, he realized there was no company to call—a moment that crystallized what a decentralized network actually means in practice.
How the Fee Problem Was Solved: Efficiency and the Lightning Network
Fees have since collapsed. Sending ¥10,000 today costs roughly ¥10—cheaper than a convenience-store ATM fee and a fraction of the ¥3,000 or so charged for a bank international wire. Bitcoin is now among the cheapest remittance rails available.
Two developments drove this. First, engineers improved how many transactions are packed into each block (each block holds around 4,000 transactions). The old structure left wasted space—like a box stuffed with unnecessary packing material—that has since been cleaned up.
The second and more transformative change is the **Lightning Network**. Instead of recording every transaction on the blockchain, two parties open a private payment channel and keep a shared internal ledger. They accumulate transactions between themselves and only broadcast the final net balance to the blockchain when they close the channel. The analogy offered in the episode: rather than settling scores after every hand of mahjong, you tally everything up at the end of the day.
Fraud prevention is built into the protocol itself. Every payment message exchanged between two Lightning parties contains information that would allow the counterparty to claim *all* of the cheater's funds if that party ever tries to submit an outdated channel state to the blockchain. It is a mutual-assured-destruction arrangement—the same logic as nuclear deterrence—and it enforces honesty without any central authority.
Stablecoins as an Alternative
Stablecoins—cryptocurrencies pegged to the dollar, yen, or another fiat currency—appear to sidestep Bitcoin's volatility problem entirely. A contract to receive ¥10 million in three months stays worth ¥10 million. Fees are relatively low. Many observers, including one of the show's hosts at the outset, concluded that stablecoins are the practical winner and Bitcoin's role as a payment medium is essentially over.
The episode also notes a striking career arc: the executive who led Facebook's Libra (the proposed global digital currency) now runs a Lightning Network payments company.
Guest Kato-san's Philosophy: Bitcoin Maximalism
Kato-san (加藤さん) from Nihon Bitcoin Sangyo K.K. (日本ビットコイン産業株式会社) joined to make the case for Bitcoin as money, not just as a speculative asset.
On volatility, he disputes the premise. Currencies such as the South African rand fluctuate as much as or more than Bitcoin; the comparison to a stable fiat baseline is misleading because many fiat currencies are themselves unstable.
On fiat stability more broadly, he walks through a historical arc: in the Meiji era, one dollar equaled one yen. Decades of inflation—especially the chaos of the postwar period—eroded that parity dramatically. Governments, he argues, have a built-in motive to inflate: it shrinks the real cost of sovereign debt. The Bank of Japan's long run of near-zero interest rates, in this reading, is partly explained by the need to keep debt-servicing costs manageable. A side effect is that cheap money flows into low-productivity businesses, dragging down the overall efficiency of the economy.
Bitcoin, by contrast, has no monetary policy. Its value is set entirely by free markets. For Kato-san, that is its defining virtue.
Ideology, Not Technology
The sharpest exchange in the episode came when the hosts raised a concrete concern: a sudden jump in interest rates could wipe out small manufacturers and spike unemployment. Kato-san acknowledged the disruption but held his position—businesses that cannot survive market-rate interest should redirect their efforts, and he expressed confidence that Japanese people's ingenuity would see them through.
The episode's final takeaway: whether you support Bitcoin as money is less a technical question than a philosophical one. It comes down to how much you trust free markets versus central-bank management of the economy. The hosts brought Kato-san in precisely because this is a domain where facts alone do not settle the argument—your prior beliefs about markets and monetary authority determine where you land.
Takeaways
- Bitcoin's transaction fees have plunged from ¥2,000 to send ¥1,000 in 2018 to roughly ¥10 per ¥10,000 transfer today, making it one of the cheapest remittance options available.
- The Lightning Network settles transactions off-chain in a private ledger and records only the final balance on the blockchain, with a mutual-assured-destruction fraud-prevention mechanism that requires no central authority.
- Support for Bitcoin as money is ultimately an ideological stance—trusting free markets over central-bank monetary policy—rather than a purely technical argument, which is why reasonable people reach opposite conclusions from the same facts.
This article is edited from a machine transcript of the first 30 minutes of the episode. It is not an official summary — please listen to the episode itself.