Its in-game description reads "Host to the blessed power of the goddess Athena." This armband is very powerful but it's not really balanced : it only have high Flame and a high Exorcism stats, but charged projectiles of magic can compensate this with little effect. You can only find the Athena's Armlet in dungeons' chests : you can't invent it or buy it. This brassard is a medium-tier weapon (Tier 6) : it will gain 4 Synthesis Points (SP) per level-up.