  Ethereum and its standardized token interface have formed decentralized
finance (DeFi), an open financial system based on blockchain smart contracts.
The DeFi ecosystem has become richer with the introduction of DeFi
composability projects, such as Lido finance and Curve finance. DeFi
composability denotes the concatenation of DeFi services in which each DeFi
service locks assets as collateral and gives another asset as liquidity of
locked assets to providers. Providers use the tokens given for other
concatenated DeFi services, such as lending, decentralized exchanges (DEXs),
and derivatives. The DeFi ecosystem uses ERC-20 tokens which can represent the
value of an asset. ERC-721 non-fungible tokens (NFTs) are not widely adopted in
DeFi, since they represent rights to an asset and are not considered
appropriate for valuation. In this paper, we propose a new concept, perpetual
contract NFT, which exploits perpetual future contracts in the cryptocurrency
derivatives market. Unlike futures contracts in a traditional derivatives
market, in the cryptocurrency derivatives market, most futures contracts are
perpetual. In addition, the value of futures contract is backed by collateral.
Therefore, if we mint the rights to perpetual contracts as NFT, we can use the
perpetual contract NFT as collateral for DeFi composability. To validate our
proposal and its profitability, we experiment with the position NFT of Uniswap
v3. Through validation, we show that our concept works in real-world scenarios.
