Probably Kira Nerest. An amnesiac whose home village was destroyed, who lived in fear of the person who took everything from her, one Kirari Arceneaux, and the sadistic tendencies she felt. She was a strange person who most others avoided, except for her commanding officer, Monika Sydow.

Through their travels together she eventually discovered that the person who destroyed her village was her. In her former life, so to speak, she had been a rogue noble from an opposing country out to "make memories" by torturing people to death in increasingly inventive ways. Her rampage only stopped when she made a mistake experimenting with her powers of bodily control: attempting to seize direct control of someone's brain. The ensuing power struggle left her consciousness in her victim's body, and her victim's consciousness in hers, with her memories and Aia's soul lost in the fray.

She managed to cling to a sort of bootlegged morality in her new life, after discovering her identity, through the human connections she hadn't ever really made before. Eventually, she made a deal with, well, essentially God, to recover Aia's soul in exchange for something. Due to the nature of Love in this universe, and the twisted actions of the current Goddess of Faith and Love, she needed a replacement for the latter with sadistic tendencies. Kirari gave up her existence and became the new Goddess, with everyone she ever knew forgetting she existed, the only trace of her being journals she left behind and a note left in Monika's pocket to let her find them. Kirari, now Kartia, will spend the rest of eternity atoning for her cruelty.