The Vault comes with Plus. It holds everything of value that isn't a bank: the house, the car, the coins, the papers that prove you own any of it.
Why it isn't just another account
Accounts is a ledger. It answers what you have to spend, it updates constantly, and on Premium it fills itself in from a bank you connect. The Vault answers a slower question, which is what you own, and the answer changes a few times a year at most.
Keeping them apart means your running balance never quietly includes the value of your car, which is the kind of number that makes a budget look fine right up until you need cash.
What goes in one
An item has a kind, a name and a value, and you can attach the paperwork that goes with it. The value is yours to set. Nothing tries to guess what your car is worth, because a guess printed as a figure gets believed.
It feeds Net Worth
What the Vault carries counts in your net worth, the one number at the top of your home, beside your Spaces and your accounts, so it isn't a separate total you have to add up yourself.
Who sees it
Nobody but you. The Vault is personal, the way money is personal in Buhata, and the server refuses to write a financial record into a shared Space at all.