Auras (Elements in Japanese version) are a brand new feature in Hatsune Miku: Project DIVA X. They are known to be important in Cloud Request Mode. There are only 5 auras, those being; Classic, Cute, Cool, Elegant and Quirky. In Hatsune Miku: Project DIVA X, things such as Modules and accessories give off different auras. When a module and/or accessories share the same aura as the song you choose, you'd receive voltage bonuses.
Each song included in the game has its assigned Aura. After completing all songs in said Aura, you unlock the medley for it.