I bought a notebook on the way to the café.

It was a small thing - cloth cover, graph paper inside, the kind of notebook people use for bullet journals and calorie counts. I told myself it was for groceries. I knew it wasn't. Moolah had promised we'd set up my first wallet that afternoon, and some instinct I didn't want to examine too closely said: you're going to want to write things down.

The café was one of those narrow Tokyo basements where the coffee is good and the air is always faintly damp. We'd moved indoors for the first time - the bench had rained on us the week before. Dev was already there, drumming his fingers on the table in a way that suggested he had been drumming them for some time. Moolah was sitting on the banquette beside him, reading a menu upside down with what appeared to be genuine interest.

"Priya." She looked up. "Did you bring the phone?"

I pulled it out. My hands, to my mild embarrassment, were slightly damp.

"Before we touch anything," Moolah said, "I need you to understand what a wallet actually is. Because it is not what the word suggests. The word 'wallet' is a marketing decision, and a bad one."

"So what is it?"

"A wallet," she said, "does not contain your money."

I waited.

"Your money - whatever money means here, your tokens, your coins - lives on the blockchain. The shared notebook. Remember?" I nodded. "The wallet on your phone doesn't hold any of that. It holds a key. One specific key, which opens one specific lockbox on the blockchain, and the lockbox is where your money lives."

She took a long sip of her latte, which, as usual, had appeared in front of her by means neither Dev nor I could account for.

"Picture a wall of mailboxes. Thousands of them. Every mailbox has a glass front - anyone can walk past and see what's inside. That's the blockchain. Everything in every box is public. But each mailbox has a lock, and only the person with the right key can open the door and take things out. Your wallet is the key. The mailbox is your address. The money is inside the mailbox. The wallet and the mailbox are not the same thing."

"So when I send Dev ten dollars -"

"You don't send him anything. You use your key to update the shared notebook so that ten of your dollars now sit in his mailbox instead of yours. Nothing moves. The ledger changes. That's all any of this ever is."

Dev, who had been nodding along, finally spoke. "Tell her about the other kind of wallet."

"I was getting there." Moolah turned back to me. "What I've described - where you hold the key yourself - is called a non-custodial wallet. Your key, your money, your responsibility. The alternative is a custodial wallet, where some company holds the key on your behalf. An exchange account, for instance."

"Like a bank."

"Like a bank. Which has upsides - they'll help you if you forget your password, they'll freeze fraudulent transfers. And downsides - they can also freeze your transfers, lose your money in their own bad bets, or, on a sufficiently bad Tuesday, simply vanish." Her whiskers twitched. "There's a phrase in this industry. Say it with me, Priya. Not your keys -"

"Not your keys," I said, "not your coins."

"Again."

"Not my keys, not my coins."

"Good. You will hear that phrase approximately three thousand more times in your life. Write it down."

I opened the notebook. Dev watched me uncap the pen with the expression of a man watching his child take their first unsupported steps.

"Now," Moolah said, "the key itself is a long string of numbers. Unrememberable. So instead, your wallet will give you a seed phrase - twelve words, sometimes twenty-four, in a specific order. Those words can regenerate the key. Anyone who has those words has your money. Full stop. No exceptions. No appeals."

"Like a password."

"Worse than a password. A password can be reset. A seed phrase cannot. If you lose it, your money is gone forever - still sitting in the mailbox, visible through the glass, but with no key in the world that can open the door. If someone else gets hold of it, they can empty the mailbox and there is no authority on earth that can stop them or get it back."

"That's…" I looked at my notebook. "That's terrifying."

"Yes," Moolah said. "Which is why we're doing this properly."

She walked me through the installation. I tapped. I confirmed. When the app showed me twelve words on a pale grey screen, she stopped me.

"Do not take a screenshot. Do not photograph. Do not email. Do not type them anywhere that is connected to the internet. Write them in your new notebook. In the order shown."

I wrote. My handwriting looked strange to me - too careful, almost calligraphic, the way you write something you expect to still exist in fifty years.

"Now." Moolah's voice was gentle. "That notebook. You are going to put it somewhere safe. Not your desk drawer. Not a sock. Somewhere that will survive a house fire and a burglary. Some people use a fireproof safe. Some people engrave the words into a thin sheet of steel. Some people split the phrase in half and store the halves in two different cities. All of these are reasonable. None of them are paranoid."

Dev cleared his throat. "I lost one, once."

I looked at him.

"Not a lot of money on it," he added quickly. "But. Yeah. I wrote the seed phrase on a Post-it, and then I moved apartments, and -" he made a small disappearing gesture with his hand. "That was real money. It's still sitting in that mailbox. I just can't open it anymore."

"And will sit there," Moolah said, "until the end of the blockchain. Which is to say, possibly forever. Dev's Post-it is a small and permanent monument to why we do this carefully."

We finished the setup. I have a wallet now. An address - a long string of letters and numbers that Moolah assured me I could share freely, the way I'd share an email - and a key that I had, for the first time in my life, written down on paper and committed to protect with something approaching my own life.

It felt oddly solemn. Like signing a lease. Like being handed something breakable.

Dev bought the coffees. A small dead leaf had somehow found its way into his cup. He didn't notice.

"Same bench next week?" he said.

"Indoors again," Moolah said, "if it rains. But yes."

Outside, the first real cold of the season was starting to set in. I put the notebook in my inside coat pocket, where I could feel its small weight against my ribs the whole walk home.