Whether you have to pay tax on an airdrop hangs on a single question: did you do something for the coins? If you had to post on a social network, fill in a form or hand over data going beyond your wallet address, you have other income from services, and that is subject to income tax from 256 euros in a calendar year. If, by contrast, the coins landed in your wallet without any action on your part, the inflow itself is not worth any income tax, but it can fall under gift tax law. That distinction does not come from a law firm's reading, it is set out word for word in the current circular of the German Federal Ministry of Finance on crypto assets.