Weapon Attributes are a game mechanic introduced in Fire Emblem Warriors. Weapons can come with attributes in some or all of their available slots and can be added or removed through forging. An attribute that is removed from a weapon will disappear while weapon used to forge an attribute onto a different weapon will also disappear. Only weapons of the same type can be forged together.
Weapon attributes are bonus effects applied to the weapon they are equipped. Each weapon can have up to six attribute slots available, with the seventh extra slot reserved for hard locked bonus type advantages certain weapons possess, i.e., Bows always have Wingslayer applied to their seventh bonus slot and the many forms of the Falchion always have Dracoslayer applied in that same slot. A eighth bonus slot exists as well, but only for character specific weapons to house their True Power/Divine Favor bonus damage.
Some attributes require a certain number of kills to unlock, while others cannot appear as an option until earned through completing History Mode challenges. Each weapon type also requires their version of the attribute to be unlocked, for example: No tome can have the Mountslayer attribute until the Unsaddler Tome is unlocked.
Several of the type of attributes are limited in the number of them that are allowed per weapon, regardless of available weapon slots. Only two from either the swap and bonus type are permitted per weapon and only one per attribute type of the defeat, focus, boost, slay, and spirit attributes.