All of my works adopt the ERC-721 token standard. This standard provides functions such as transferring tokens between multiple accounts, obtaining the current token balance in an account, obtaining the token owner, and obtaining the total number of tokens supplied on the network. There are several types of token standards of Ethereum, but ERC-721 is a token standard suitable for issuing NFTs and most major projects adopt this token standard. The reason is that it is possible to assign a unique ID to each token, which enables NFTs to have the characteristic of being unique and valuable. However, there is also a downside of requiring high fees. Another standard that is widely adopted is ERC-1155, which is an excellent token standard that combines the features of ERC-20 and ERC-721. However, it is not possible to assign a unique ID to each token. On the other hand, it has the advantage of being able to send multiple tokens in one transaction, resulting in low fees.