The main protagonist and the "16-year-old robot" to which the title refers, a state-of-the-art sentient gynoid automaton created by Dr. Noreen Wakeman five years prior to the series, though she was designed as a 16-year-old girl. Though XJ-9 was designed to be Earth's protector, armed to the teeth with a wide range of weapons, devices, and transformations, she desires to live the life of a normal teenager and often makes this desire quite apparent to her friends and creator.
- Action Girl
- All of the Other Reindeer
- Amazonian Beauty: Though you can't tell from the character designs, XJ-9 is 6 feet tall, according to Professor Wakeman's specs.
- Badass Adorable
- Balloon Belly: She inflated more than once, despite being made of metal.
- Bare Your Midriff: Her chassis design is meant to mimic this, complete with a large exposed screw for a "belly button".
- Beware the Nice Ones
- Bratty Teenage Daughter: To Nora sometimes.
- Cool Loser
- Cute Bruiser
- Cute Machine
- Do-Anything Robot
- Does Not Know Her Own Strength
- Fem Bot
- Genki Girl
- Girlish Pigtails
- The Heroine
- I Just Want to Be Normal: Combined with I Just Want to Have Friends: Being a superpowered robot wouldn't be so hard for her if there were more bots as advanced as her.
- Jerk with a Heart of Gold/Nice Girl: She often shifts between these depending on the episode.
- Magic Skirt: Justified, that skirt's made out of metal.
- Pinocchio Syndrome: Averted - she's perfectly fine with being a robot, but wants acceptance and assimilation... which sometimes means playing the trope straight.
- Power Gives You Wings: Jetpack wings to be exact.
- Red-Headed Heroine: Once had red body paint, and her makeshift human form is a redhead.
- Ridiculously Human Robot
- Robot Girl
- Robot Hair: She sports a pair of metal pigtails.
- Super Strength: "The strength of a million-and-seventy men," if the theme song is to be taken literally.
- Surprisingly Good Japanese: Helped by the fact that her VA Janice Kawaye is also Japanese.
- Telescoping Robot: She provides the trope picture.
- Wake Up, Go to School, Save the World
- Younger than She Looks: Technically has been alive for about 5 years, but has all the mentality of a teenage girl... usually.
- However the fact that Jenny being physically five years old, has had a drawback of being forced to be in Kindergarden for the majority of the episode "I was a Preschool Dropout".
- You Gotta Have Blue Hair
Voiced by: Chad Doreck
Jenny's best friend and next-door neighbor.
Voiced by: Audrey Wasilewski, Jess Harnell
Brad's little brother.
An elderly spinster robotics scientist and the one who built XJ robots, who is often simply refers to as "Mother" or "Mom" by Jenny and her sisters.
Sheldon Lee/Silver Shell
Jenny's self-proclaimed romantic admirer.
Jenny's "sisters" XJ-1 through XJ-8
XJ-9's prototypes and "sisters".
Voiced by: Eartha Kitt
Voiced by: Audrey Wasilewski