your account -- and the one irreversible thing you can do to it
Start the tutorial again from the first step. Steps you've already done tick themselves off straight away, and achievements you've already earned stay earned.
This permanently deletes your company and your account together -- there's no way to have one without the other (see "Deleting your account" in the README if you're curious why). Once this completes, there's no undo, no recovery, and no support request that brings any of it back.
Gone for good: your cash, every building and its level, your entire warehouse, any open listings or bids on the Market (and whatever cash or resources were escrowed in them), every division and piece of infrastructure you've bought, and your full tick-by-tick and balance-sheet history. Your login itself goes with it -- this same email can sign up again afterward, but as a brand new company starting from scratch, not a way back into this one.
The one thing that survives is a permanent record that this email and this company ID once existed and were deleted -- nothing about what either of them actually had.