It's either built up from the Pocklekul or from the Thorn Armlet, and it should have abilities, such as ABS UP, Poverty or Wealth, but if you buy the Moon Armlet in a shop, it won't have any special abilities. Its in-game description reads "Highly magical armlet made from the Moon Stone." It's got a high Chill and Scale attribute meaning that it's effective against fire-based enemies or reptiles, and you can also charge it so it's a quite powerful armband for Monica. This armlet is a medium-tier weapon (Tier 6) : it'll gain 4 Synthesis Points (SP) per level-up.