God of War's Runic stat boosts all forms of magical damage. Frost explosions from throwing the axe, extra elemental damage from your weapons, and of course runic attacks themselves. Special skills you purchase with experience will indicate they do extra elemental damage (for example all caps, 'FROST'). The runic stat governs the damage of those types of skills, along with frostburn that you inflict when your weapon powers up from consecutive hits with the permafrost skill. It looks like defense is relevant here as well. Since defense covers ALL forms of damage (the game lacks direct elemental damage resistance) having extremely low Runic will result in you not being able to overwhelm enemy defenses and deal the full damage of your runic attacks. The further your runic is from their defense, the more damage you'll do. At lower runic (relative to level, such as 80 runic vs 160 for a level 6+ Kratos) the extra damage from frostburn is negligible, while it really comes into its own when you have a much higher value. Great attacks like glaive storm will take chunks off even Travelers with high runic.