Kyoko is a young teenage girl, with a slender and short build. Despite being the younger sister of Ryohei she doesn't seem have any traits in physical appearance, and she is described as a rather cute girl, especially by Tsuna. She has short golden brown hair (which is colored blonde in the manga on certain occasions), with bright golden eyes. Sometime during the Curse of the Rainbow Arc, Kyoko's hair was now shorter, without any given reason.
While consistently changing outfits in the series, her most prominent outfit is her Namimori Middle School uniform. She wears a white formal shirt, a dark sweater vest with a red bowtie, a gray skirt, black knee-high socks and brown shoes.
Her future counterpart has much longer hair that reaches down to her back, she wears a dark green hooded jacket and a light green dress underneath.
While far from stupid, Kyoko is a somewhat air-headed girl that lives a mostly carefree life in Namimori, she doesn't seem to question many of the odd occurrences in her life, such as the idea of an infant being a hitman in the mafia, or being sent ten years into the future, which she often assumes are school activities or harmless jokes, to the point where she even believes in what her older brother tells her when he receives an injury, even if they sound too ridiculous to be true.
She is a kind and caring girl, always looking out for her older brother and her friends. Kyoko is rarely ever shown to get angry at other characters, with some of the rare occasions being towards Kensuke Mochida, who claimed that she was a "prize" during Tsuna's kendo match against him, and when Tsuna and his guardians refused to explain the mafia and Millefiore Famiglia to Kyoko who had no idea why she was trapped in the future, in which she temporarily went on strike and refused to cook and clean until she was given an explanation. Kyoko has a fondness for sweets, taking the third Sunday of every month and having an appreciation day where she eats as many cakes as she wants.
- The name Kyoko means "capital city" (京) (kyo) and "child" (子) (ko).
- Kyoko's surname Sasagawa means "bamboo grass" (笹) (sasa) and "river, stream" (川) (kawa/gawa).
- In the Card Games Kyoko is attributed to have Mist Flames.
- She is the most popular girl at Namimori Middle School.
- In the anime, when she was a kid, her dream was to be a ballerina. She wants to become the prima and dance in Swan Lake in France. She also said that if that didn't work out, she'd like to become a police officer and catch bad guys.
- Although the degree to which Ryohei and Kyoko's parents are involved in their lives is unknown, a glimpse of what may be a father is shown eating a meal with them during a flashback Kyoko has.
- Ryohei states that to this day, Kyoko thinks boxing is two guys fighting in their underwear with oven mittens on.
- Kyoko had long hair up until preschool.
- In the manga, she was shot by the Dying Will Bullet on two different occasions.
- As stated by Tsuna's father, Nana Sawada was similar to Kyoko when she was young.
- Every third Sunday of the month, Kyoko decided she can eat as much cake as she wants. This is the same for Haru who named the day "Haru Appreciation Day."
- In a 2016 ranking, 500 Shonen Jump readers (split evenly between men and women) were polled on the heroine they hate the most. Kyoko placed 20th out of 45 alongside Aika Hiiragi (M×0), Kyōko Inaba (Jigoku Sensei Nube), and Ina Kawai (Magical Taruruuto-kun).
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- Katekyō Hitman Reborn! Fate of Heat II - Unmei no Futari
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