Kaidou Kio (海堂 貴緒 Kaidō Kio) is an art student and a friend/classmate of Agatsuma Soubi In volume 6 who is claimed to be one of Soubi’s only friends. Most of his early dialogue is filled with flirtations and passes towards Soubi, despite being ignored or rejected each time. In addition to his flirtations, he also is often accusing Soubi of being a loli-con, or pervert, for his relationships with Aoyagi Ritsuka and the male Zeros. Kio is fascinated by Soubi's art, this is what drew him to Soubi in the first place but in the manga, he stated that the bandages on Soubi made him curious of him. He admires Soubi's style and skill and desired friendship from the first time he saw one of Soubi’s paintings. Kio is friendly and lighthearted. He is a flirt and a self-described pacifist.
Kio has a large tattoo of a butterfly on his back (it was recently revealed that Soubi only became interested in Kio due to a tattoo on his back, and a vow he took when he got it) and earrings covering both ears.
Kio’s quirks include his sweet tooth, his love of piercings/tattoos and his habit of calling people by nicknames and the suffix "-chan." He frequently makes sexual innuendos. He gives Soubi Agatsuma an ear-piercer for Ritsuka to use on his Fighter. Kio comes up with nicknames for most people (Sou-chan for Soubi, Ricchan for Ritsuka, the Chibis for Sagan Natsuo and Sagan Youji, etc.) and sometimes refers to himself as Kio-chan.
Despite his early presence as a character who exists solely to create a lighter atmosphere in a very dark story, he gradually gains depth as the series progresses. He becomes an adult voice to champion pacifism and self-worth, contrasting greatly with Soubi’s submissive nature that willingly accepts violent treatment and his strong desire to be controlled by others.
Kio is shown to be extremely stubborn in his beliefs in chapter 45 when he opts to stay outside in front of Seven Voices Academy instead of going to the safety of the hot springs. Because of this choice, he is kidnapped.
[ - rewrite paragraph about kio being insightful with quotes from vol 2 (fear in soubis eyes) and vol 6 (communication) rewrite paragraph about kio's work ethic]
In volume 7, chapter 45, Kio says that he is quite possibly Soubi's only friend. He and Soubi often make jokes together, spend time together at school in the studio, and at Soubi's home.
Despite being quite aware that Soubi lives a life quite different from his own, Kio does not know the details. Kio laments that he thought he would finally know Soubi's secrets when he was being pulled away from entering the academy.
Kio and Ritsuka meet in volume 7, chapter 44. Kio appears quite angry when they meet, however he is impressed with Ritsuka's manners. Kio had expected to meet another person much like Seimei Aoyagi.
When Kio sees how upset Ritsuka is at hearing that Seimei was a bad and violent person, he doesn't take his words back, but he does apologize for upsetting Ritsuka and offer to comfort him. At this point, he decides that Ritsuka is very different from Seimei and he can start to like Ritsuka. He then starts addressing Ritsuka without an honorific... and soon after, Ricchan.
"Ritsuka, you and I are kindred spirits. I gave up on Soubi too. But giving up doesn't mean turning your back on him, it's just acceptance."
The Male Zeroes
Kio does not hide his hatred for Seimei from anyone. This includes Ritsuka who he lets know immediately when they meet, that he hated Seimei.
Kio has an intense hatred for Aoyagi Seimei and continuously reaffirms his opinion throughout the story. Eventually, he warms to Seimei’s younger brother Ritsuka when he realizes how pure the boy is and that Ritsuka is responsible for Soubi becoming ‘human’ again. Although he’s pleased with this change, however, he is also very jealous of the relationship Ritsuka and Soubi have, and often calls Soubi a pervert or warns others of his Lolicon (sexual attraction to younger girls) behavior.
Kio was kidnapped by Nisei and held hostage by Bloodless. while Soubi and Ritsuka were at the Seven Voices Academy. Kio was used by Seimei as leverage to get his own fighter, Nisei, back after he was taken captive during Beloved’s attack on the school. While in Bloodless’s custody Kio was baited and belittled but the thing that would stick with him most during this incident was not the cruelty he was treated with
While held hostage, Kio received a visitor who he remarked could be mistaken for his twin. She then refers to him as "Big Brother Kio." She identifies herself as Chouma.
Kio is stunned by this encounter and upon being rescued from capture he retreats to the Kaidou household. A wealthy home that is only for the women in his family. Kio goes to seek advise from his daughter, Shikiko, a girl between the ages of ten to sixteen without ears (whom Kio must refer to as Shikiko-san.) Kio asks her if he has a sister and is told that "it was before [Shikiko’s] time."
While visiting her, Kio remarks how he doesn't feel like the girl's father, partially because of their close ages and partially because of her formal and mature additude. Shikiko appears to be jealous of Kio's attention to Shieko (Shikiko's mother) and Kio appears olivious to this.
Shikiko muses on her father’s “weakness” and how he must be kept safe, while he is visiting her mother.
Kio goes to visit Shikiko’s mother, a quiet woman named Shieko, who Kio speaks to from his knees. When knocking on the door he jokes that he is "the florist." He presents her with flowers, she is dressed formally and traditionally and they meet in a sparse room where she sits on a cushioned bench. Kio approaches her to handher the flowers and then backs away, to sit closer to the door on the floor and says that he will "sit over here, so it is okay." This is not explained but is backed by the context of the home being matriarchal and Kio's complex relaitonship with the members of the home which is vauge.
- The name Kio means "valuable" (貴) (ki) and "thread" (緒) (o).
- Kio's surname Kaidou means "sea, ocean" (海) (kai) and "hall" (堂) (dou).
- Kio is almost never seen without a Chupa Chups, a type of lollipop produced in Spain that comes in a large variety of flavors.
- Kio hates the sound of a lollipop being bitten.
- It takes Kio (a self-proclaimed expert) 10 minutes to finish a Chupa Chups.
- Kio's favorite Chupa flavor is Pudding and then Cola.
- Kio has part time work as a nude figure model for drawing.
- Makes no appearances in vol 4.
- Before having hotpot with the Zeros and Soubi, Kio offers to return a key to Soubi's house that he had borrowed and quote, "no longer needed."