"You said you wanted to fight adult tyranny, I heard that the Code Module contains information on every Kids Next Door operative, who knows what Father can do with information like that. Now's your chance to stop him, now's our chance."
Numbuh 83, or Sonia, is a KND operative. She is the "Soda, Snacks, and Treats Officer" of Sector W. She is a friend of Tommy Gilligan (from his days training at the KND Arctic Training Base and Prison), Numbuh 84, and Numbuh 85.
Sonia's usual outfit is a pink and white blouse, a cerise flounce skirt, purple earrings, pink knee socks and purple T strap Mary Janes. She has blonde hair put up in pigtails, with the hair holders being cerise. She also wears two purple bracelets on each of her wrists.
Sonia is a very cheerful and outwardly girl that always looks at the bright side of things and works with her friends to accomplish a mission or task.
Despite her cheerful personality, Sonia has a much darker side that she unleashes whenever she experiences fear. In Operation: T.R.A.I.N.I.N.G., when Father's henchmen tried to put her in a dark cell room, Sonia went ballistic and unleashed an angry and monstrous personality and mercilessly beat up her captors even as they begged for mercy. Both captors were badly bruised, had black eyes, and knocked out teeth. After her fit of rage, Sonia simply replied "What? I don't like the dark.", as her typical cute self.
Sonia was introduced in Operation: T.R.A.I.N.I.N.G., where she, Tommy and Lee undergo training from Numbuh 60 at the KND Arctic Base and end up single handedly defeating Father when an unexpected surprise attack occurs. In Operation: D.A.D.D.Y., she helps Lee and Numbuh 1 prevent Shaunie from getting an awful haircut. She also appears in Operation: Z.E.R.O. where she is seen in the art museum. She plays a role in Operation: I.N.T.E.R.V.I.E.W.S., alongside fellow Sector W members Lee and Harvey, to take part in the Delightful Children's scavenger hunt. At the end of the scavenger hunt, she is the person who calls out Harvey for not caring about anything other than winning, and lets Sector V take all the stuff her sector had found.
- Sonia's defining characteristics are her beauty, her fear of the dark, and her violent, almost demonic temper, despite her outwardly nice and shy behavior. In Operation: T.R.A.I.N.I.N.G. and Operation: D.A.D.D.Y., she enters a violent rage and beats up a villain when they threaten to lock her in a dark room.
- Sonia seems to have a crush on Lee and vice versa, as the 2 were seen holding hands in Operation: Z.E.R.O..
- Sonia is voiced by Janice Kawaye, who is also Ami from Hi Hi Puffy AmiYumi, Kim and Kam from Class of 3000, and Jenny from My Life as a Teenage Robot.