The key is a golden Celestial Spirit Key, with the bow of the key being sculpted with the heads of Gemi and Mini, two circular faces with two dots for eyes and boomerang-shaped mouths, one in a smile while the other one in a frown. The sides of the bow features an arm from each of the twins protruding. The blade of the key ends in a design similar to a harp.
While in possession of the key, a Celestial Spirit Mage may be able to summon the Twins Gemini by reciting the quote, "Open the Gate of the Twins! Gemini!". This summons a pair of humanoid Celestial Spirits capable of transforming into other people, granting them access to the transformed person's Magic and memories.