**4.2 Ethereum-based Metaverse**

The Metaverse is a three-dimensional virtual space where social and economic activities are commonly used just like the real world. NFT plays a role of mediating interaction and proving private property within the Metaverse world. An example of NFT application is the CryptoKitties. It is a blockchain-based cat reproduction game. CryptoKitties is an Ethereum ERC-721 token-based DApp [11]. Game users are given only one cat in the world in CryptoKitties. Cat digital assets have a rarity because they contain a separate unique recognition value, unlike existing virtual assets. In general online games, when the service is terminated, there is a problem that the character developed in the game can no longer be owned. However, digital assets with NFT technology can be distributed and stored by individual participants connected to the network to prove ownership.

Decentraland implemented the concept of real estate in the Metaverse by combining virtual reality and blockchain technology [12]. Decentraland made it possible to purchase land, a virtual real estate, using MANA, an ERC-20 token. Users can freely place buildings on land purchased from Decentraland, earn income by attaching billboards to buildings, or open exhibitions by collecting rare digital content. Land ownership and other collectible items are ERC-721 non-fungible tokens. These unique assets are made through Ethereum smart contracts and allow owners to prove ownership on the blockchain ledger. Cryptocurrency MANA can be purchased on exchanges and can also be used to purchase digital goods and services around the world.

Enjin Coin is a cryptocurrency project created for game item trading, and is an integrated platform for creating blockchain-based games. Enjin is a smart contract platform based on the Ethereum blockchain, and is a protocol and cryptocurrency that supports the crypto needed to create, manage, and implement virtual goods for game developers, content creators, and game communities. Ethereum-based ERC-20, ERC-721, and ERC-1155 token items can be stored and managed in a mobile cryptocurrency wallet. Enjin Coin guarantees the ownership and currency value of game items used in all games. When Enjincoin is applied as a currency in Metaverse, it can be used not only as a currency in Metaverse, but also in the real world with the value of currency.
