Weapon Fusion is a gameplay element used only in Knights in the Nightmare. Weapon Fusion can be accessed on the Setup Screen under the Items category. Two of the same weapon can be fused together, which will produce an item with their combined DUR. Keep in mind that when one item has a higher quality value than the one it is being fused with, the new item will adapt the lower quality value. Fused weapons can keep fusing with others if so desired. Item fusing reduces clutter and creates room for more items, in addition to reducing the need to replace weapons that have been used up.

Enhancement failures on fused weapons are less costly due to their generally higher Durability, which is decreased by one (1) when a failure occurs.