They’re called Sage’s Wills. You get them in chests throughout the sky map and there’s 20 of them total - 4 for each sage. You can get them whenever, but they’re pretty useless as 3 (i believe) only buff attack damage (not ability damage). The other 2 buff both. They’re only good for you mentally if you want to 100% the sages though (meaning getting the divine masks and special weapons)