|“||You guys go back if you want, but I'm leavin'. ... I'm not about to stick around in this fucked-up place any longer than I have to. Screw the others; I'm outta here! ... Hell yeah I'm serious! Those assholes are the ones who chose to stay behind. They're just gonna die one by one, and I say let 'em!||”|
—Kai Shimada, Corpse Party: Book of Shadows (Episode #7; 『Tooth』)
Kai is a teenage boy of average height and build. He has spiky, somewhat long red hair, and cyan eyes. He wears the standard Byakudan Senior High School uniform, with both the shirt and blazer fully unbuttoned with the sleeves rolled up, and a black shirt underneath. He also has multiple black armbands on his right forearm, a belt with a gold buckle, a silver earring on his right ear, a black choker with a silver pendant with a blue gem and wings, and a gray watch on his left wrist.
Kai is a red-haired high school student who stands out in the same class as Yuuya Kizami. He is a model for a popular men's magazine, known as Men's Buckle. In contrast to the quiet and behaving Yuuya, Kai is loud, foul-mouthed, and rude, often going around intimidating his fellow classmates and committing acts of vandalism; however, he's also popular among girls for his looks. He is rather selfish, shown to be willing to abandon his friends to save his own life without a second thought. He is a notorious womanizer, and it is rumored that he has as many as ten simultaneous girlfriends.
Kai is also incredibly arrogant, frequently boasting about his characteristics, and describing himself as "Mr. Perfect," and a "real renaissance man." Fitting with this, he can also act rather eccentric, and often exaggerates what he does and says, dubbing Yuuya his "moral enemy", coming up with almost absurd ways of beating him and bursting into fits of maniacal laughter seemingly at random. He is a very sore loser and despises those who are weak or stand up to him. He holds a particularly fierce grudge against Yuuya. As a result of all these traits, Kai is either feared or disliked by the majority of ordinary students, though he isn't unpopular per-say.
However, Kai is very much aware of the negative view people have of him, and seems genuinely upset by this, claiming that he works hard behind the scenes and that there is "more to him."
Kai's corpse can be found in the second chapter in main hall on the first floor, next to Tomohiro Ohkawa's and Masato Fukuroi's remains. According to his name tag, he died from hemorrhaging after being sliced with an edged weapon. He calls out Yuuya's surname upon examining him for the first time.
Kai is briefly mentioned by Tomohiro when he meets Yoshiki Kishinuma. Tomohiro mentions that Yoshiki and Kai have the same intimidating look in their eyes, to Yoshiki's confusion.
Kai also appears in the extra preview "Tooth," having mostly the same storyline as the Corpse Party: Book of Shadows episode of the same name.
Corpse Party: Book of Shadows
Episode #7; 『Tooth』
Trapped in Heavenly Host, Kai is grouped with Yuuya, Ryosuke Katayama and Tomohiro, later joined by Tohko Kirisaki and Emi Urabe. As Ryosuke has been seriously injured, he tells Emi to go ahead and search for traps. However, he ends up going himself when Tohko and Yuuya go in her place.
As they walk around, they find the infirmary. The door is closed, and Kai finds the key, but then he loses it while carelessly tossing it in his hands. They find the entranceway next and realize that the door is open. Tohko suggests going back to get Ryosuke and the others, but Kai attempts to scout ahead and abandons the others. He sweet-talks Tohko and asks if Tohko wants to join him, which angers Tohko, prompting her to yell at Kai. As Tohko heads back, Kai takes out his knife and threatens Yuuya, much to the latter's amusement. Tohko is rejoined by Yuuya while on her way.
Later, Tohko returns to the entranceway while looking for Mitsuki Yamamoto and running away from a ghost; Kai is nowhere to be seen, however. Afterward, she and Emi hear his footsteps. When they finally see Kai, he slumps down on his knees, and the laughter of children echoes around. Tohko then realizes that he has a knife stuck in his abdomen, leading to Kai's death. As Yuuya joins them, a ghostly girl dressed in red suddenly appears, and they run away. Afterward, Yuuya collects the knife from Kai's body after pushing Ryosuke down the stairs and uses it to kill his remaining classmates.
Corpse Party -THE ANTHOLOGY- Sachiko no Ren'ai Yūgi ♥ Hysteric Birthday 2U
#1; The Shame on the River Kwai
Kai first appears at the beginning of the chapter. He, along with Yoshiki, protest against the romantic comedy Sachiko has planned, although for different reasons, with Kai saying that the main protagonist should be someone with his characteristics, instead of Satoshi Mochida. When Sachiko announces a race, in which the person to reach the goal gets to leave with a person of their choice, Kai is the first person to volunteer. He calls to Tohko and tells her that if he wins, he'll pick her to come with him and that she should "reward him" when they get back.
Afterward, Kai starts running despite no signal being given, in order to get ahead of everyone else. He runs out of the auditorium, and almost immediately slips and falls down a hole to his presumed death, as a penalty for starting too early.
#8; Today's the Day, Farewell
Kai appears with all the other characters at the end of the day, when Sachiko asks everyone to go swimming with her. At first, Kai refuses to go, saying Sachiko was just laughing at everyone's pain. However, he does end up going with everyone, and even comments on Sachiko's new necklace, calling it cool. Afterward, he is sent back into the closed spaces with everyone else.
Corpse Party: Blood Drive
EX CHAPTER 03『The Unconceding』
Kai appears as the main character of the third extra chapter, which focuses on him and his efforts to defeat Yuuya. It begins with him introducing himself and bragging about his looks, money, and ways with women. However he is interrupted by Yuuya, who bumps into him, but barely acknowledges it. Annoyed, Kai sets off to find some dirt on him, and after overhearing a conversation between Tomohiro and Ryosuke, he gets the idea to find Yuuya's weakness.
Afterward, he bumps into two male students. Kai grabs one of them and threatens to beat them up for not apologizing. He lets them go though, and he finds a group of girls talking about him and Yuuya. They comment on how smart, tall, and mature Yuuya is, but call Kai a "bad egg". Kai yells at them, and they run off. Afterward, there is a choice to either go to Kai's classroom, or the student council room.
If Kai chooses to go to his classroom, he sees Tohko and Emi talking, and spies on them from outside. At first, they talk about a girl's magazine, but then the topic changes to Yuuya. Tomohiro and Ryosuke later join in, and they wonder if he's bad or afraid of anything. Emi mentions how Yuuya was more expressionless than usual when dissecting frogs, and suggests he may not be good with animals. The bell then rings, and they leave to go to their class.
If Kai chooses to go to the student council room, he abruptly walks in on Masato and Mitsuki Yamamoto, to Masato's dismay. Kai asks Masato about what Yuuya doesn't like, and Masato says that Yuuya doesn't like helping Kurosaki at his part-time job, which is at a horror-themed shop. Mitsuki however, gets suspicious and asks Kai about his motives. Masato tells her to calm down, and Kai agrees, saying that she'll get lines on her perfect forehead, but he does like the way she looks when she's angry. He then kisses Mitsuki on the cheek, and goes, leaving a raging Mitsuki and Masato.
After school, while Kai is walking home, he sees Yuuya ahead of him. He shouts at him, getting his attention, and challenges him to a fight, saying he will never lose to the likes of him. Depending on where Kai went earlier, the following scene changes:
If Kai went to his classroom, he throws a small green frog, which Yuuya easily catches. However, the frog doesn't bother Yuuya, so Kai reveals a cat from behind his back. This is also unsuccessful, so he retreats, vowing that there will be a rematch.
If Kai went to the student council room, he would get ready to fight Yuuya, but then suddenly starts telling a horror story about three boys exploring a haunted house. By the end though, Yuuya is actually interested in the story, and Kai leaves furiously.
The next day, Kai walks into the student council room and is shocked to see Yuuya there. Masato warns him not to start a fight when Kensuke Kurosaki shows up with some R2 yakisoba bread. Kai challenges Yuuya to a bread eating contest, and lays out his terms: if Yuuya wins, he gets the cover shot of the next issue of Men's Buckle, and if Kai wins, Yuuya must kneel before him and admit he's a loser. Yuuya agrees, and he, Kai, Kensuke, and Masato take a bite. Kai, unfortunately, gets the red hot chili sauce piece, and cannot hold in his screams. Yuuya declares himself winner, but then goes still. Kensuke scolds him for pushing himself too far and accidentally reveals Yuuya's allergy towards parsley. Kai immediately mocks him and declares the match a draw. He gets a call from work, and is about to leave when Yuuya provokes him by calling him a mongrel. Furious, Kai once again challenges him, ordering Kensuke to buy some egg bread. Kai loses yet again and is forced to give Yuuya the cover shot, which ends up increasing the magazine's sales by over 30,000 copies.
Afterward, Kai stands on the roof, depressed as he wonders if Yuuya can be beaten. However, he regains his confidence, saying that the battle has just begun, and swears that next time he'll have Yuuya begging for mercy, and begins laughing maniacally.
Corpse Party: Coupling X Anthology
"A Dark Gray Portrait"
While Eiko Matsuno is walking through Heavenly Host, she comes across, to her horror, Kai masturbating. Noticing her in her ball form, he grabs her, noting her as red human soul, while Eiko screams at him to let her go. Intrigued, Kai wonders if she is telling him something, and squeezes her, much to her discomfort.
After Eiko manages to escape, she later bumps into Sakutaro Morishige, and accidentally sends him an image of Kai masturbating.
Kai holds a deep grudge against Yuuya, which stems from Yuuya's popularity amongst the other students, due to his impressive physical ability and subtle charisma. Kai has repeatedly challenged Yuuya, only to be beaten each time, and is shown to devote much of his time to the sole purpose of defeating Yuuya. Even in death, his spirit can be heard groaning Yuuya's name.
The rivalry is, however, entirely one-sided, and Yuuya himself doesn't consider Kai a threat of any kind and finds his persistent efforts both amusing and annoying.
In his "Soulful Testimony" for Corpse Party: Blood Drive, Kai's voice actor Manabu Sakamaki suggested that Kai's hatred for Yuuya has come full circle to becoming a twisted kind of love.
Kai seems to be infatuated with his classmate Tohko. In Book of Shadows, he asks her to come with him, saying he doesn't want to see her die, and that she is "precious" to him. It's unknown if he has genuine feelings for her or simple lust. Tohko herself hates Kai, despising his terrible attitude.
Masato is the only known person to address Kai by his first name, suggesting he is closer to Kai than his other classmates. Masato shows concern when Kai eats a chili yakisoba bread and warns him not to focus too much on his job. Likewise, Kai seems to ask for Masato's advice in his schemes frequently and promises to catch up with whatever school work he misses.
Shreds of Kai's "more to him" can be seen in his interaction with Tomohiro in Corpse Party: Book of Shadows. When Tomohiro is crying, torn over whether to leave his injured friend Ryosuke, Kai, exasperated, announces he will leave in his place. When Tomohiro tries to thank him, Kai, not wanting to seem soft, quickly adds that nothing will get better if Tomohiro leaves since he is a "worthless sack" and a "waste of space." Later, when Kai groans about how useless Tomohiro is, Tohko mentions that he still volunteered to go in place of Tomohiro, so clearly he does hold some concern for the well-being of his classmates. This renders Kai temporarily speechless, before laughing it off, calling them all nuts.
- Kai's PSP and Vita voice actor Manabu Sakamaki is the same VA for Shougo Taguchi.
- In his extra chapter, Kai frequently makes reference to Greek mythology, describing himself as an "Adonis," and claiming that "Gaia" is on his side.
- Kai is one of Sakuya Kamishiro's (the main character designer and illustrator for the series) favourite characters.