AniFi World uses Gacha system (or random) heroes when players mint heroes. That means players have many chances to receive same heroes to achieve your target hero (Especially if players need high rarity heroes). Making duplicated heroes to be not useless, AniFi World applies rank (or star) system to enhance your hero's abilities.
The ranks will be from 0 star to 5 stars. When players minted a hero, players will receive 0 star hero. For the duplicated heroes, players can dispose the heroes to receive Hero dust to use as a material to upgrade your hero rank.
The amount of Hero dust for upgrading depends on hero's rarity and rank.