Sally Simpson holds the role of Executive Officer for the Council Unit in Londinium, reporting to Tommy Walker. She possesses light orange hair, usually secured in a ponytail, and matching orange eyes.

Her key duties encompass military command and direct oversight of Londinium's Watchtower, humanity's final defensive bastion against the hostile Earless. Operating on the front lines due to the city's vulnerability to constant brutal Earless assaults, she also manages responsibilities concerning the welfare and supervision of Londinium's children.

During a mission alongside Tommy to retrieve Mu from Gnome, Sally openly disapproves of his decision to execute Field Marshal Ace, revealing a clashing moral stance. After the Listeners kill Tommy, she shifts allegiance. Sally accepts aid from Denka and actively forges cooperation with the Listeners, signaling a pivotal change in her alliances and role.