The capital cities of Pandaemonium and Sanctum are the only locations for the Armsfusion Officer, who will charge a fee to fuse weapons. Talk to in Pandaemonium or in Sanctum. Rates are based on the weapons' rarity and level, and will be displayed in the Fusion Cost box. There is no failure rate for armsfusion. The fusion can be undone, retaining only the primary weapon by Armsbreaking.