Spell Runes are mystical inscriptions the Nightmare Spell leaves on an Awakened's soul. They form a unique signature: Aspect, Flaw, unlocked abilities, current rank.
Reading
An Awakened can consult their own runes to evaluate their progress. Certain rituals (notably the public Awakening) reveal runes to a vetted circle.
Shadow Bond Sharing
Sunny's Innate Ability Shadow Bond lets him read his master's Spell Runes — a massive strategic advantage in the secrecy of the Forgotten Shore.
Narrative Importance
Spell Runes are the equivalent of a character sheet: what changes them changes the bearer. Any change (ascension, Aspect evolution, Flaw incident) rewrites the runes.