item:dungeons_gear:emerald_chestplate and item:dungeons_gear:opulent_chestplate and item:dungeons_gear:gilded_glory_chestplate and item:dungeons_gear:opulent_helmet and item:dungeons_gear:emerald_helmet trigger some hidden mechanic of the mod "touhoulittlemaid". When I equip one of above and move toward any directions, it keeps spawning one item of "touhoulittlemaid".

Hmmm, they're dropping emeralds as you walk around, based on a loot table. Possibly that mod overrides emeralds?

Confirmed. Touhoulittlemaid is replacing dropped emerals with another item. You can adjust the loottable for Lucky Explorer to change what it drops in a modpack with both mods.