Well, I don't like giving that much away for this thing, but I don't see any other choice. Trading the trident is completely out of the question. Trading the blade is stupid for obvious reasons. The rabbit dress is too important as a backup plan for entering Eientei, and the hand mirror is too important as a transformation time-saver.
Hopefully the value we're losing here can be more than made up later, once we have a complete sword.