A powerful construct mage of Cosmo Entelecheia that specializes in water and ice techniques. Fought Nagi Springfield with Secundum, Tertium and Nii eight years after The Great War. Septendecims seems to be a quiet person since she has only been seen speaking to chant her spells and to tell Secundum that Nagi was alive after their attack. She appears to be of the demi-human species, and is able to cast the highest level of ice-magic spells, Kosmike Krustallopegia ("Frozen World"), a spell only seen from Evangeline.
- Like her companions, her name is derived from numbers, and in this case from the latin word for "seventeen", which means that she was the seventeenth generation of her kind.