Proserpina

Proserpina (プロセルピナ) is a Magic God of Roman Mythology and a member of the true Gremlin, first mentioned in Shinyaku Toaru Majutsu no Index Volume 13.

Etymology
is the Roman goddess of the Underworld, her Greek equivalent being. A daughter of the agriculture goddess Ceres, she was abducted by Pluto, god of the Underworld, to be his wife. Her distraught mother searched desperately for her daughter, letting the crops wither away in her grief. Jupiter eventually had Pluto release Proserpina but because she ate the food of the dead, she couldn't completely return to the world of the living. As a result, she spends six months with her mother and six months with her husband, resulting in the changing seasons.

Magic God Invasion Arc
At some point around the time of the incident instigated by the High Priest, Proserpina encountered Kamisato Kakeru and was 'exiled' by his World Rejecter.