Demeter is the goddess of the harvest and agriculture in Greek Mythology. She is the daughter of Cronus and Rhea, who presided over grains and the fertility of the earth. Though Demeter is often described simply as the goddess of the harvest, she presided also over the sacred law. Demeter was intimately associated with the seasons.
It was believed that Demeter made the crops grow each year; thus the first loaf of bread made from the annual harvest was offered to her. She was the goddess of the earth, of agriculture, and of fertility in general. Sacred to her are livestock and agricultural products, poppy, narcissus and the crane. She is the mother of the Spring goddess Persephone.
When Hades abducted and married her daughter Persephone to be his wife and queen in the Greek underworld, she punished the caretakers of Persephone into monsters. Then in a fit of anger and sorrow at her daughter's loss, Demeter laid a curse on the world that caused plants to wither and die, and the land to become desolate.
Zeus, alarmed for the barren earth, sought for Persephone's return. However, because she had eaten the pomegranate while in the underworld, Hades had a claim on her. Therefore, it was decreed that Persephone would spend four months each year in the underworld. During these months Demeter would grieve for her daughter's absence, withdrawing her gifts from the world, creating winter. Her return brought the spring.
Demeter restores the protagonist in the Womb of Grief following his mortal wounding at Alex's hands, calling him by the nickname "My Harvest" and imploring him to grow into strong and healthy wheat. In exchange for his resurrection, she asks that he aid her in collecting fruits from the Mothers and Wardens of the Womb.
She lacks physical power, admitting to being weaker than a pixie, but makes up for it with her powerful healing capabilities and non-combat magic that can hide her and the protagonist from others. Demeter is on friendly terms with the mothers (Anahita and Ishtar being the first) who are both prisoners and protectors of the fruits, and is set on her course no matter what happens as she reveals with her talk to Maria. Should Alex die near the end of the original routes with Amon's fruit she will lament the rotten state of it, cursing humanity for destroying it and hoping they all die horribly on Neutral and Chaos. On Law she is saddened, but supports Zelenin and the protagonist for their path before vanishing.
She reveals her true nature on the New/+ routes, where she takes the fruit away from the protagonist and reveals her true role as a servant to The Three Wise Men alongside fellow servant Mastema. She laughs at the fate that shall befall them on Chaos/Neutral+ and the killing of Mem Aleph or offering her sincerest gratitude in Law+, before leaving for the Empyrean Ascent on all three. Her true motives unveiled by Louisa Ferre.
Demeter appears during the final battle as Shekinah summons her, telling her to offer her life for a world of Law. Fearing her own death and inability to bring fertility to the world under the God of Law, she reluctantly complies and uses her full healing powers, the "Eleusinian Harvest", her life withering away as she laments and dies. Her healing power now bestowed upon Shekinah as her essence is absorbed.
Demeter portrays herself as childish and innocent to hide her true nature, a ruthless agent of Law who has to rely on others due to her lack of power, even having a sadistic streak and amusement at the actions of others. Her loyalty to Law and desire to bring fertility is genuine. Demeter's willingness to serve means she was even willing to sacrifice her brother Zeus using the protagonist, and eventually, her own life, to make the world of Law a reality.