Some viewers of the cosmos might see the Three Realms and notice a forth secret realm, the Other Realm. The Other Realm is a hidden world linked to the Mortal Realm. It is the home of the Fey and other usual beings who thrive on trickery, fear and confusion.
The Other Realm's place in the cosmos is sometimes unclear. The GM decides if their version of the cosmos includes the Other Realm and where it sits. They have three options:
The Other Realm does not exist, or is so well hidden it might as well not. It is unnoticeable and untouchable.
The Other Realm forms part of the Mortal Realm, even if most mortals are unaware of this. While Fey are not Mortals, they, and their realm, will also be destroyed should the Mortal Realm be.
The Other Realm is adjacent and separate to the Mortal Realm. It is a forth realm in its own right and will have a stake in the great war as one of the potential victors, or losers.
The group should be informed of which option is chosen. If option 2 or 3 is chosen, then see below for lore on the Other Realm and the Fey.
The Other Realm is a strange and whimsical place, full of strange and whimsical creatures.
Instead of virtues, they choose emotions?
emotion (eMOTIONAL DAMAGE!)?
memmories
Forged or cast iron is instinctively repulsive to fey. The reasonings why are widely debated. Some say an ancient archfey was so disgusted by the destruction and violation of the natural earth that they cursed its existance, inadvertantly spreading their disgust to all fey. Another theory suggests the magnetic nature of ferrous metal can attract or repel a fey's supernatural essence away from their corporeal form.
Regardless, the effects on fey are severe enough to be a serious threat to even the strongest fey.
An important fact is that impurities in the metal appear to weaken its effect. An iron sword is more effective against fey than a steel one.
You have a weapon specially designed to harm fey.