Nephthys was a resident of Midesta and a close friend of the Shamar Freedom Fighters. Under the threat of the Eggman Empire, she chose to join the Egg Army to keep the people safe from Dr. Eggman, but still keeping some control over the region for the doctor. The Shamar Freedom Fighters followed on part, acting as the opposition to the Midesta Egg Army to give the people hope, but secretly trying to keep balance with the Egg Army for Nephthys. (StH: #279)
Following the discovery of Gaia Temples and their Gaia Key guardians, Nephthys kidnapped resident guardian Ehsan and held him hostage at her base in Shamar. During one night, the Knothole Freedom Fighters Sonic the Hedgehog (in his Werehog form), Antoine D'Coolette, Chip, and Big the Cat assisted the Shamar Freedom Fighters in infiltrating Nephthys' base to rescue Ehsan. However, as part of their plan with Nephthys, the Shamar Freedom Fighters lured each member into a trap, with Nephthys and her Egg Army cornering Sonic. The two engaged in battle, during which Nephthys tried to convince Sonic to abandon any effort in trying to stop Eggman, as opposition will only encourage Eggman's wrath. Sonic ignores her demands, proclaiming that he will not rest until he defeats Eggman for everyone's sake. While the others rescued Ehsan, Sonic managed to disable the Egg Boss and regroup with the others. Following the battle, Nephthys recuperated from her brawl and contacted the Shamar Freedom Fighters over her failure in the mission, but assures them that they can still salvage the power balance in Midesta. (StH: #278, #279)
Hunting Eggman's Enemies
She team up with Maw, where they both had to face off monsters.
Keeping with the Egg Boss aesthetic, Nephthys appears serious and territorial towards her enemies with the intent of regional domination. But underneath, Nephthys is a motherly, compassionate soul who believes Eggman to be unstoppable; to provoke him is to doom everyone else. She is protective towards her friends and innocents, and was willing to become an Egg Boss to keep Eggman from taking over by perpetuating an eternal stalemate with the Shamar Freedom Fighters. Nephthys is also modest and takes full responsibility for complications that arise, even when in the face of Eggman himself.
Nephthys is capable of gliding with the use of her cape, but without it appears to be ineffectual. She can use this as an advantage when battling grounded opponents for aerial strikes and evasion.
- Nephthys' name comes from Egyptian mythology, where she is a goddess protector of the dead and associated with Set, god of the desert.
- Nephthys is the fourth female Egg Boss to be introduced, and like her three predecessors is exclusive to the Post-Super Genesis Wave Timeline.
- Nephthys' species, specifically Egyptian Vulture, was revealed by Ian Flynn on the BumbleKing Forums. 
- According to Aleah Baker, Nephthys is 42 years old.