In Fire Emblem Fates, Thoron is the personal tome of the avatar from Fire Emblem Awakening; Robin. It can only be obtained by scanning the Robin amiibo and it cannot be removed from his inventory. However, Thoron replicas are available whenever Robin is manning the armory in My Castle, though they are not as powerful as the original.
Thoron is a special move of Robin in Super Smash Bros. for Nintendo 3DS and Wii U. It is the final form of Robin's Standard B move which takes 5 seconds to charge. Thoron appears exactly like it does in Awakening, manifesting as an extremely quick, horizontal bolt of lightning. It can pierce through multiple targets.