What is "chthonia"

In Greek mythology, the name Chthonia (Χθωνία "of the earth") may refer to:

• Chthonia, daughter of Erechtheus and Praxithea. She was sacrificed by her father, who had received a prophecy according to which he could win the imminent battle against Eumolpus only if he sacrificed his daughter. Her sisters, who had sworn to kill themselves if one of them died, fulfilled their oath by throwing themselves off a cliff. According to the dictionary Suda, only two of the sisters, Protogeneia and Pandora, did commit suicide, which makes sense since of the other daughters of Erechtheus, Orithyia had been abducted by Boreas, Procris married off to Cephalus, and Creusa was still a baby at the time the oath had been sworn. It was also said, however, that Chthonia married her uncle Butes, which probably indicates a version that she was not sacrificed.
• Chthonia, daughter of Phoroneus or of Colontas. She and her brother Clymenus were said to have founded a sanctuary of Demeter Chthonia (see below) at Hermione. In another version, Demeter, during her wanderings in search of Persephone, was ill-treated by Colontas, against which Chthonia protested. Demeter burned Colontas alive in his house, but saved Chthonia and transported her to Hermione, where she founded the aforementioned sanctuary.
• Chthonia, one of the Alkyonides.
• Chthonia, an epithet of Demeter and several other chthonic deities, such as Hecate, Nyx or Melinoe.

Chthonia was also an ancient mythical and poetical name of Crete. Chthonia is and was also a fictitious planet and story setting in the story Ready Player One, in which a character called James Halliday creates a Dungeons and Dragons setting here.