Talent Materials
In order to max a character's talent levels, players will need Talent Level-Up materials - scrolls or books you can get from different domains across Teyvat. These will permanently boost your characters stats in the game.
Talent level up materials can be crafted using alchemy by combining lower-level talent items to create higher level ones. For example – if you want to level up Keqing’s Combat Talent, you need Prosperity books which can be obtained by completing Taishan Mansion, the Domain of Mastery located in Liyue.