Yes, you can.
If you summon the NFT character and the character currently in use is not an NFT character, the better character is updated as an NFT and the other character is converted into character pieces that can be used to upgrade your NFT character.
You can also choose which skills to keep from the two characters.
However, if you are already using an NFT character in the game, the other NFT character cannot be summoned right away. You must seal the NFT character in use in order to summon the other NFT character.
* If the number of the converted character pieces exceeds the limit, the rest will be added as Mileage.