Star Dress: Aquarius Form is one of several forms of the Star Dress Spell.
Lucy takes on an appearance based on Aquarius' own, aquiring a bikini top that sports a zigzag design; frilled, dark sleeves that are secured around her upper arm by a ribbon; and a frilled, dark miniskirt; around said miniskirt is a ribbon that is tied in bow to keep it secure. Additionally, Lucy's hair becomes tied up in pigtails and she is given sandals to wear. Aquarius' zodiac sign is located between Lucy's collarbone whilst in this state.
Water Magic (水系各種魔法 Mizu Kei Kakushu Mahō): After sacrificing Aquarius' key to summon the Celestial Spirit King, Lucy was bestowed the Magic of Aquarius by the Celestial Spirit King, which allowed her to both consciously and unconsciously make use of her friend's powers.