パスト

One of three people called "Ghosts", that chase Scrooge and Carol for some reason. Past's abilities are unknown. He is an Endlave pilot whose entire identity is concealed within his specially customized unit. His Endlave was not built for mass production, but has been modified heavily and given stronger destructive power, and is considered overkill for any practical military operation. 

From url=http://en.wikipedia.org/wiki/List_of_Guilty_Crown_characters#Guilty_Crown:_Lost_Christmas.

Its body already had cancer when it was assigned to operate the Endlaves Kestner, Fleischmann, Recknagel, and Eden Bebe. The latter, Eden Bebe, was assimilated with Past's spirit after it finally lost the body to the apocalypse cancer./

Past's identity is the biological mother of Mana and Shuu. Despite that by now she is nothing but a spirit (literally), she has preserved the intention to protect her children. She aims to find the source of Mana in the Lost Christmas by prowling Scrooge until he reaches it./

Translated from the url=http://ja.wikipedia.org/wiki/%E3%82%AE%E3%83%AB%E3%83%86%E3%82%A3%E3%82%AF%E3%83%A9%E3%82%A6%E3%83%B3#.E3.80.8E.E3.83.AD.E3.82.B9.E3.83.88.E3.82.AF.E3.83.AA.E3.82.B9.E3.83.9E.E3.82.B9.E3.80.8F.E3.81.AB.E7.99.BB.E5.A0.B4Japanese .