Trance Twins appear on floors 3-5 in Yukiko's Castle in the Midnight Channel. They may drop Wonder Cloth when defeated. Selling 8 Wonder Cloth at Daidara will unlock the Survival Guard unisex armor in the shop inventory.
During Quest #10: Extracurricular Activites, the history teacher, Ms. Sofue, will ask the protagonist for help finding material for a new dowsing rod. Defeating Trance Twins at this point will cause them to drop the Suspicious Pole item. They will continue to drop this until the quest is completed.
Trance Twins appear on the fourth and sixth floors of Yukiko's Castle within the Midnight Channel. They will attack using physical strikes and Bufu, but also will stand by for a turn with a warning that they are gathering magic power, after which they will use Mabufu. Selling 6 pieces of the Wonder Cloth it drops will unlock the Survival Guard unisex armor at Daidara Metalworks.