Kyoko is somewhat carefree and air-headed, not questioning the idea of an infant being in the Mafia and believes whatever Ryohei says as his reason for his injuries even when it clearly sounds too ridiculous to be true. She is kind and caring, always looking out for her brother and her friends and tries her best to help them by cooking for them or tending their injuries.
Kyoko looks quite different from her brother. She has short golden brown hair and bright honey eyes. In the future, her hair is longer and she wears a dark green jacket with a light green dress beneath it.
When Kyoko was a child, Kyoko was used as a bait to lure out Ryohei by upperclassmen who disliked him. As a result, Ryohei was injured that left a scar on his head to protect her, making Kyoko feel guilty. Not wanting to see Ryohei hurt again, she asked him not to get into fights again, something that Ryohei promised but is unable to keep to this day due to his position as the Vongola Sun Guardian.
In the beginning, Kyoko is Tsuna's only reason for coming to school. From her very first appearance, she is established as an off-filter character. When she is named as a 'prize' by Mochida when he challenges Tsuna to a duel, she attempts to lunge for him, but her friends hold her back. During the Daily Life Arc, she proceeds to participate in many of Tsuna's wild antics. She has, as of this point in the story, been shot by the Dying Will Bullet twice: the first one was when she played Russian Roulette and the second one was when she ate one of I-Pin's Gyoza Buns, falling unconscious and being shot by Reborn to be saved. She visits Tsuna's house while Gokudera is still under the effects of the Ten-Year Bazooka after Giannini tinkered with it, and assumes that Gokudera's child form is Tsuna's little brother. Tsuna hastily lies that the child Gokudera is his cousin, prompting Kyoko to remark that she doesn't see her own cousins often. She later observes Valensa & Toras trying to assassinate Tsuna and assumes that they are burglars.
Kyoko was not involved in any of the fighting. She does appear during the List Countdown when Ryohei is attacked by Ken. She buys the story that he climbed the chimney to the bathhouse and received a "sprain" when he fell. She also believes Ryohei when he explains to her that the gauze, his broken arm, and missing teeth are all just part of the "sprain."When Tsuna and his friends encountered Birds in Kokuyo Land, the latter shows them video of Haru, and Kyoko and Hana were stalked by his subordinates the Bloody Twins, and threatened to order the twins to kill them if Tsuna don't listen and do as he says. However, she and Hana were saved by Shamal while Haru was saved by Future Lambo and I-Pin whom Reborn had requested to watch over them.
At the end of Tsuna's flashback due to the Criticism Shot, he hears her being reassured by Ryohei that Tsuna will come back, so she agrees and states she had total faith in him.
Kyoko accepts Ryohei's story that he, along with the rest of Tsuna's Guardians (though he doesn't use that term), are just participating in a series of sumo-wrestling matches over the course of the next seven nights. She doesn't like it, but she accepts his reasons for coming home so badly beaten. She also takes care of Lambo with Haru and Nana after Lambo is badly beaten in the Lightning Ring Battle. Before the Sky Ring Battle, Kyoko gives Tsuna a handmade charm and wishes him good luck for the sumo-wrestling match.Millefiore. An attack made by Nosaru and Tazaru of the Millefiore makes her fall to a nearby warehouse. The younger Tsuna stumbles in however, Kyoko calling him "Tsu-kun", but before Tsuna can do anything, Kyoko is replaced by her younger self by the Ten-Year Bazooka. She witnesses Tsuna transform into his Hyper Dying Will Mode and witnesses him get hurt; however, Tsuna utilizes his Zero Point Breakthrough to defeat Tazaru. She is escorted back to the Vongola Base along with the younger Haru, Lambo, I-Pin, and Yamamoto by Gokudera and others. Later, concerned for her friends and family and feeling trapped inside of the base, she locates an unobserved exit and finds her way into the city, successfully avoiding capture by the Millefiore and taking shelter with Hana until Tsuna comes to find her. Kyoko and Haru volunteer to do the housework while Tsuna and his friends train. Kyoko and most of the other non-fighting characters stay behind in the invasion.
In the week leading up to the Choice game, Kyoko and Haru demand Tsuna that he tell them everything about the Mafia, Byakuran, and the Millefiore. While Bianchi, Fuuta, Giannini, I-Pin, Chrome, and Reborn support them, Tsuna refuses to admit to them that there was anything worth knowing; as a result, Kyoko and Haru go on strike by refusing to do any housework while being kept in the dark.
She eventually recants, and on her way to buy groceries to cook food for everyone, she is stopped by Tsuna (who was misled by Bianchi to believe she had run away again). Tsuna realizes on the way to stop her that there is a difference from being kept completely in the dark and knowing there is something that others are refusing to tell a person; so, he sits her down and tells her everything. She is then able to offer her opinion as to why Tsuna's Sky Vongola Box was being temperamental, which gives Tsuna a clue on how he needs to open the Box Weapon correctly.
During the first Choice battle, she and everyone (except the participants) were watching the fights from the audience stalls.Skull, but was saved by Hibari's hedgehog. Afterwards, she told Tsuna that Chrome hadn't come back and wanted to consult him about it. The next day, they all decides to check on Chrome once again on Kokuyo Land, meeting Ken and Chikusa on their way and was informed that Chrome has came back, but acting weird. Seeing Chrome's condition, Kyoko, Haru, I-Pin, and Yuni decides to stay to comfort Chrome.
On the afternoon, when Tsuna and the others returns to Kokuyo Land once again to check on them, they are held captive by Daemon Spade within a sphere that slowly draining their oxygen, waiting Tsuna and his friends to come to save them. Once Tsuna and the others succeeded, back at home, Ryohei attempted to convince Kyoko to stay in the past and not getting involved in their final battle with Byakuran, but Kyoko refused, telling him that she can't stay still while the others are fighting. Seeing how determined she is, Ryohei accepted her answer.
When Ryohei was about to get into a fight with Koyo, Kyoko happened to passing by Tsuna's house and heard the word "fist" that Ryohei said, questioning does he intend to fight, which Ryohei reluctantly answered that he is not. She then supported Ryohei when Nana suggested that they should have studying competition instead of fighting.
She is seen again with Haru at their usual cake shop, buying some cakes, seen by Tsuna. Reborn asked Tsuna if he wants to approach them before fighting against Simon Family, but Tsuna doesn't want to involve them again and leaves, quietly saying goodbye to them. Kyoko suddenly states that she feels warm, most likely barely sensing Tsuna's presence.
After one week has passed since the battle at Simon Island, Kyoko comes to school to see her Ryohei, in a net due to Adelheid's punishment for him breaking the rules; she was worried about Ryohei because of his injuries from a supposed "shooting star", afraid of him reopening his wounds, much to Tsuna's disbelief at the obvious lie Ryohei gave her.
When Chrome transferred to Namimori-Middle, Kyoko was happy to welcome Chrome, but then surprised when Chrome suddenly hugged her, worrying her. Chrome then told her about her situation, so Reborn suggested for Chrome to stay at either Kyoko's or Haru's house until they found a place to stay for her. After school, Kyoko, Haru, and the Simon Family attends Chrome's welcoming party at Tsuna's house, with Kyoko and Haru becoming moral supports for Chrome. After the second day of the Representative Battle, Kyoko arrives and greets Tsuna and his representative members, causing Tsuna to question her presence. Kyoko explains that Chrome wasn't at school that day, and that she found Chrome feeling unwell in her apartment and took her to the hospital for a checkup. Kyoko then reveals that the analysis stated that her internal organs were gone. Tsuna recalls that that once happened in the future. Kyoko tells Tsuna that despite her grave condition, Chrome seemed to want to talk to him, always calling out for "Boss."
Kyoko's final appearance is with Haru and Tsuna's Guardians, standing outside Tsuna's house as they wait for Tsuna to join them for celebration of Tsuna's tutelage, invited by Reborn.
- In the Card Games, Kyoko is shown to have a Mist Flame; however, this has not been confirmed by the creator of the series.
- She is the most popular girl at Namimori Middle School.
- 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 her dream doesn't come true, she'll become a police officer and catch bad guys.
- Ryohei states that to this day, Kyoko thinks boxing is two guys fighting in their underwear with oven mittens on.
- Akira Amano stated that Kyoko had long hair before preschool.
- In the manga, she was shot by the Dying Will Bullet on two different occasions.
- As stated by Tsuna's father, Iemitsu, Nana was similar to Kyoko when she was young.
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