Celesdue is the Guardian of the Moon.
Wild Arms 3
Celesdue's Medium name in Wild Arms 3 is known as the Moon Spark, which is one of twelve Mediums. In this entry, she is depicted as a goddess wearing a long purple ribbon standing upon the moon. She uses gravity powers to lift up and drop all of the monsters on-screen, and her Arcana and summoning do massive amounts of damage to enemies without an elemental weakness, such as the King of Angolmois at Lunatic Garden and Dantalion in Gunner's Heaven's Master League.
Wild Arms 5
Celesdue's Medium in Wild Arms 5 is known as the Moon Medium, which is one of six Mediums. She sits upon a crescent moon, wearing a decorated quiver full of arrows and holding a staff that can become an archer's bow. When summoned, she shoots an arrow down to Filgaia and inflicts every enemy-occupied hex with debuff effects. Interestingly, she fires the arrow at the summoner during the animation, but the summoner isn't the one affected. Rather, the summoner is being given the power to inflict the debuffs on the enemies by Celesdue.