Affects ALL elemental damage, including Blue Magic, Weapon Skills and Enspells.
Especially for BLU it's a massive damage increase and by far the best belt for nuking under a certain distance to your targets, which is pretty much a given with cleaving spells like Tenebral Crush anyway. And it only gets stronger the closer you are, up to +15% damage.
While this is a neat Elemental Magic/Weapon Skill piece it is massively overpriced for what it does.
Compare this to the Hachirin-no-Obi or any of the given Elemental Obis.
~ 10% bonus for magic of the day
~ 10% bonus for magic matching single weather
~ 20% bonus for magic matching single weather and day
~ 25% bonus for magic matching double weather
~ 35% bonus for magic matching double weather and day
This basically means that even getting a tier 1 Storm spell from anyone /SCH gives a +10% Damage Dealt bonus regardless of distance (so it's better for Leaden Salute by default if you're shooting rather than melee'ing).
Since it's getting more common, SCH mains giving tier 2 Storm is +25% Damage Dealt, almost double the maximum of the Orpheus. The only situation Orpheus levels the field in is if you're using the Hachirin Obi and the day opposes the element you're using. Using the single element Obi instead will fix this.