Writing a novel involving Bitcoin - Help Needed!

Hi r/Bitcoin ,

I'm currently writing a fictional story, the central drama of which is that someone hid a flash drive containing hundreds of Bitcoin behind a puzzle involving geocaching, CTF-type online games, and cryptography. I am wondering what exactly needs to be hidden to keep the bitcoin inaccessible until the puzzle is solved. I am new to cryptocurrency, although I have recently picked up my research on the topic quite a bit. I am aware that you can restore wallets using a seed or private key - but do you actually make a copy of your original bitcoin in that process, or just restore access to an existing wallet? Basically I need to know these things:

1. What do I actually hold when I say I own a bitcoin? Do I hold an actual file that is the string of numbers that is the bitcoin, or does the blockchain just store the data saying I own a bitcoin?
2. If I have bitcoin stored on a flash drive and air-gapped like this one would be, can I recover them without recovering the physical flash drive, if I have the seed or private key?

Thanks for your help!