Nephthys

Nephthys is the goddess of nature, lamentation, sleep, and the night. She was born on the Fifth Demon Day as the twin sister of Isis. In a later life, she married her former brother Set and became the mother of Anubis.

Background
Nephthys was originally born to Geb and Nut with her elder siblings Horus, Isis, Osiris, and Set. She was later reborn as Set's wife. She eventually had a child with him, Anubis, but gave him to Osiris to raise, claiming she did not want him to meet his father. Anubis himself is skeptical of this, believing it was because he was "different". When Set tricked Osiris and trapped him and attempted to kill Isis (as well as an unborn Horus), Nephthys attacked Set to protect her sister and nephew, much to Set's annoyance. After Set cut up and scattered Osiris's body, Nephthys helped Isis and Horus find the pieces. Anubis then helped put Osiris's body back together using mummification and Isis used her magic to bring Osiris partially back to life.

The Red Pyramid
When Nephthys is released from the Rosetta Stone, she takes Zia Rashid as her host. Upon returning to the First Nome, however, Chief Lector Iskandar realizes who she is and, fearing for Zia's life and secretly desiring to return to the old ways, hides Zia and replaces her with a shabti. Nephthys is later able to establish a weak connection with Sadie Kane, the host of Isis, conveying to her that she is within a 'sleeping host'. Nephthys is also seen in Sadie's vision in the Hall of Ages, trying to protect Isis from Set. The shabti of Zia is eventually able to tell Sadie Set's secret name in order to defeat him.

The Throne of Fire
Nephthys is freed from Zia's body after Zia is rescued by Carter Kane. She then says hello to Bes and after apologizing for using Zia as a host, tells Carter and Bes that Zia has an important destiny and that Carter should protect her. Then she returns to the Nile, her true body.

Personality
Bast notes that she is unpredictable, but little is truly known about her. Nephthys seems to care for her sister, risking Set's wrath by helping Isis escape when he attempted to kill her. Set tells Zia's shabti, thinking it is Nephthys, that in one life, she was his treacherous sister, and in another, his treacherous wife. This is probably just how she sided against Set.

Appearance
Nephthys herself has only been described as 'slender'; since her reawakening, she presumably has kept Zia's appearance while possessing her. When she left Zia's body, she was described as having regal features, like Isis, but kinder eyes and smile. She was dressed in a blue dress and a silver Egyptian crown.

Powers and Abilities
Nephthys's powers and abilities remain unknown, but as a river goddess she can communicate through rivers, particularly if she has a connection with the one she is speaking with. She is assumed to have all the standard powers of a god. Since she is a river goddess, she can probably control water. Set says she is the weakest of the Demon Days gods.

Relationships
Set: Although there seems to be some mutual love between the two, they do not trust each other. Nephthys has sided against her husband more than once and likewise, Set was willing to sacrifice her to gain power.

Isis: Nephthys seems to love her sister very much, even willing to attack Set to protect her. She was later willing to help Isis and Sadie fight Set and keep him from destroying North America.