Chi is a small grey and white kitten with dark grey stripes across her face, cheeks, back, and tail, blending American Shorthair and grey tabby traits. Her large expressive eyes and frequent grins are distinctive. Originally named Sarah by her biological mother, Marie, she separated from her feline family during a walk, collapsing from exhaustion before Yohei Yamada and his mother found her. The Yamadas adopted her, naming her "Chi" after her early urination accidents ("shishi" meaning urine in Japanese).

She has a loud, bubbly, and charismatic personality, often behaving childishly. Chi is clumsy, rash, impulsive, and easily distracted, struggling with concentration and agility compared to other cats. She gradually forgets her past life with Marie and her biological siblings, Ann and Terry, and consistently refers to herself in the third person.

Her relationships define her journey. Blackie, a large black cat she meets early on, mentors her in feline behaviors, becoming a close friend. She mourns his temporary absence by staring at the crescent moon, reminiscent of his fur patch, and they later reunite. Cocchi, a stray white kitten with black markings, starts as a rival but becomes a close companion. They share adventures like sneaking out for food and narrowly escaping danger on a road. Though Cocchi briefly stays with the Yamadas, he leaves, uncomfortable with domestic life. Chi later plays with kittens resembling her siblings but remains unaware of their biological connection.

Chi experiences confusion about her identity, questioning if she belongs with humans or cats. She observes physical differences like her tail and ears, noting, "Chi understands Blackie’s words" while struggling with human speech. This leads to her realization: "Chi might not be one of them... Chi is the only one who doesn’t understand." Her adaptation includes learning to use the litter box, confronting fears (especially of dogs), and navigating challenges like vet visits.

During the "Summer Vacation" storyline, she travels with the Yamadas to Okinawa, encountering new feline friends like Tiida, Umikaji, and Champuru. This setting fuels her exploration, featuring adventures involving the ocean, local plants, and community interactions. Her core bonds with the Yamadas endure, marked by Yohei’s kindness, Dad’s affectionate but sometimes strained bonding attempts, and Mom’s nurturing presence. Despite forgetting Marie, Chi retains a subconscious comfort from maternal figures, reacting with confusion during their eventual reunion.

Her development across all media highlights adapting to loss, forming new bonds, and reconciling her dual identity as a cat living with humans, underscored by continuous exploration and growth.