Within the scope of a BTC ETF, the associated assets usually include Bitcoin futures contracts, Bitcoin options, as well as other Bitcoin-related financial instruments. A BTC IOU (I Owe You), which represents a promise to deliver Bitcoin at a future date, can be considered an asset in itself, depending on the context and specific regulations of the financial market in which it is being traded. However, it is important to note that the definitions and classifications may vary according to the laws and regulations of each jurisdiction.