Board Thread:Questions and Answers/@comment-30575144-20150831185926/@comment-1419424-20150831195821

You can only change NPC equipment by clearing the Crimson Orochi mission with only that NPC as an ally. Once you do, you will be able to change their equipment to Reinforced versions of whatever equipment types you cleared the mission with (i.e., the weapons you are normally able to forge using the material gained from that mission). You do not need to forge equipment for them; they will already have it.