Chia Nagasawa is the younger but taller sister of Martha.
Chia is one head taller than her older sister, with short, dark, straight hair in an asymmetrical bob cut, turquoise eyeshadow, wears a black beaded necklace and brown beaded bracelet, has facial piercings on her nose and eyebrow and gages in her earlobes, and wears a black and white baseball cap with a diamond decal on the front above the brim, a white t-shirt with rolled up sleeves with a black bullseye on it, rolled up torn brown jeans held up with a belt, and black high tops resembling those made by Vans.
Not much is known about her, other than that in most of her appearances, she's unpleasant to Martha, and usually having an annoyed attitude (usually at Martha) and a sarcastic comment for every situation.
In her own words, she's the more responsible sister, usually hinting that Martha is more foolish despite being older.
She is also often seen using her skateboard to get her way around.
Miraculous Chipmunks: Outta Time