Powerboost Armlet
パワーブーストの腕輪 [powerboost no udewa] or 'powerboost armlet' in Japanese. Note that this equip did not originate in the Final Fantasy series, but was instead added during a collaboration event with Kingdom of Swords and Magic.
Record Keeper

Powerboost Armlet (V)
Stats: ATK +20, Max Level: 1
Type: Accessory, Rarity: ★★★★
Other: during the originating event this armlet gave EX synergy
Category: Equipment