Mercury (メリクリウス Merikuriusu) is the sixth and final goddess to be introduced and is the youngest of the Jupiter Sisters. She is currently residing within Ayumi Takahara.
Mercury has a very detached personality that can sometimes be misunderstood as absolute indifference. Her personality is sometimes misunderstood because she tends to deal with the problems of others as if they are trivial things not worthy of her attention, even if said problems affect her as well. Mercury is not completely devoid of emotion, however, since she does worry about Ayumi whenever Ayumi feels troubled and even immediately apologizes if she faces admonishment, providing that she understands that she is initially at fault.
As if to complement her impartial habits, Mercury also displays herself as one that seems to be in a constant state of drowsiness. Already seen as someone who appears to require a myriad of sleep, rarely does she have her eyes fully open even when she is awake.
Like her sisters, Mercury's true appearance is not revealed. Also, similar to her sisters, Mercury appears as an altered version of her respective host, Ayumi. Her skin noticeably darkens, and in contrast to Ayumi's dark hair, Mercury's hair gets a silver-white color. She also acquires long bangs usually set aside to cover one of her fiery-red eyes, and under each of her eyes is a set of two horizontal lines. Most of the time, Mercury either has her eyes half open or completely closed, giving off a sleepy disposition.
As one of the Jupiter Sisters, Mercury also has a halo and a pair of wings.
Mercury has been referred to by her sisters as the specialist with regards to unfamiliar/bizarre spells. As such, Mercury's sisters turn to her whenever they are faced with a spell they aren't sure how to deal with, such as Apollo's hydration spell and the teleportation spell used to transport Keima and Elsie back to the past.