.mfer is a Premium decentralized identifier (DID) launched by KEY3.id, a distributed, open, and extensible naming system with the features of Assets as DID, Available for Transferring Tokens. The Mfers NFT holders can claim the corresponding numbered DID, e.g. 0000.mfer at KEY3.id. The .mfer DID is bound one-to-one to the Mfers NFT, and the DID quantity is limited to claim according to the collection's quantity.