A creature's 'element' (Light, Dark, War, Love, Memory, Satiation…). Stacking matching Aspects on your board unlocks team buffs at set breakpoints.
“A Traveler's Guide to the Planes: Aspects” — official lore art.
An Aspect is a creature's "element" — Light, Dark, War, Love, Memory, Satiation, and more. In the lore they're the world's fundamental principles, which existed as balanced opposing pairs (Love/Hate, Light/Dark) until the Sundering broke them apart.
In battle, stacking Anima that share an Aspect unlocks team buffs at set breakpoints — see the full list on the mechanics page. There are roughly 16 "playable" Aspects out of a larger lore set.