XJ-9 is the ninth robot of the XJ series, but when she discovers something downstairs in the basement, she finally realizes she has 8 "sisters," which are actually prototypes. XJ-9 is referred to as the oldest, despite being made last. As the idea of XJ-9 was conceived from each of them, she is the oldest in that sense.
The XJ robots make their first appearance in the first season episode, "Sibling Tsunami", and go on to appear in "Sister Sledgehammer", "Agent 00' Sheldon" and "Escape from Cluster Prime" (mostly cameo), and notably "Turncoats." (XJ-8 also appears briefly in "There's No Place Like Home School").
List of Robots
- Nora Wakeman built the XJ Robots to replace Armaggedroid due to him going rogue.
- My Life as a Teenage Robot is the first Nicktoon to feature a large amount of sisters in the main character's family (9), the second being the Loud House, featuring 10 sisters.