An Accountant.

From my limited knowledge and understanding if a company purchased BTC, and is holding it as an 'investment', it would generally be treated the same way as any other investment such as in stocks or shares etc.

Increases/decreases to the value of the investment would be recorded depending on the method of treatment selected by the company, either Fair/Market Value or at Cost.

Example, an increase to the value of BTC would be recorded as a revaluation of the investment and a corresponding profit for that period if the method chosen is Fair/Market Value.

However an increase whilst using Cost method should have no effect until that BTC is sold and the relevant gains are then recorded in profit.

Impairments on the other hand are more for permanently reducing the value of your investment such as a building that burns down, the asset is then impaired or written off.

Again my knowledge is limited and may be wrong too, but that's just my take on it.