In the end, even after I entered this school. Nothing had changed. No, perhaps it was that I had no intention of changing anything from the start. For better or for worse, it was the same as that time. The reason for that was very simple. ... Because I myself wanted this.
— Kei Karuizawa's monologue, Light Novel Volume 4
|Hair Colour||Gold Gradient|
|Eye Colour||Violet Gradient|
|Class||1-D (1st Year)
2-D (2nd Year)
|Affiliation||Advanced Nurturing High School|
|Light Novel||Volume 2|
|Manga||Volume 1, Room 4|
She is a prominent figure of class. Being gifted with an attractive personality, she is considered to be the girl's leader of class D. Her development in the story is worth reading. Despite her looks and attitude she displays and the relationship between her and Hirata, she has her bunch of secrets that she cannot afford to reveal to others.
Kei is a teenage girl of average height with waist-length blonde hair that is tied in a ponytail and purple eyes. Her school uniform consists of a light blue dress shirt below the red school blazer with rolled-up sleeves and a short white skirt. She walks in standard school shoes with light blue calf-length socks. She predominantly wears a blue ribbon around her collar. In a more casual situation, she simply wraps her school blazer around her waist and rolls up her dress shirt sleeves.
Kei is an outgoing person who spends most of her time with the girls at school and Yōsuke Hirata (Kei's boyfriend). Typically she speaks for the girls in the class, acting as one of the leaders along with Yōsuke and eventually Suzune Horikita.
She seems to be a bit of a mooch, as after spending all her points from the first month and D-Class not receiving any, due to their penalties, she asked the girls of her class to lend her some money to buy the 'essentials', managing to gain at least 2000 points from Kikyō Kushida.
She doesn't take notice of less prominent people in the class. This was seen when she mentioned Kiyotaka Ayanokōji being "invisible" after Suzune nominated him as guard with Yōsuke. Ironically, she befriended him in the light novels and they were very close, even being impressed by his abilities and going on a first name basis as she eventually starts to develop romantic feelings for him.
In volume 4 of the LN's, it was revealed that in her earlier years Kei was bullied in school, resulting in a physical scar and a lingering mental scar. To help prevent this happening again at her new high school, she started going out with Yōsuke Hirata, the most popular guy in class. This gave her a sense of security to just be herself without worrying about being targeted for abuse. Although this wasn't a genuine relationship, Yōsuke did know about the circumstances and went along with it to protect Kei.
Kei was assessed as being subpar by the school. Her absences and grades in middle school were direct reasons for her being placed in D-Class. She doesn't like academics nor sports, but is surprisingly able to compete with others. She has immense mental strength, according to both Kiyotaka and Kakeru.
In the anime, Kei, like the other first years, listened to the speech given by Manabu Horikita, welcoming the first years to their new school. She was seen in the class talking to Satsuki Shinohara before Yōsuke Hirata asked the class to introduce themselves, agreeing with the idea.
After the teacher Sae Chabashira walked in and introduced to the class the system in which they are supposed to live in now, Kei was surprised at the fact that they received 100,000 private points, to begin with. She was seen talking with Maya Satō and Chiaki Matsushita about clothes and jewelry shopping after the classes that day. At the start of the new month of June, along with the rest of D-Class, Kei was shocked when Class D did not receive the monthly allotment of points, looking depressed throughout the explanation of S-Points and the reason D-Class didn't get any points.
At some point later, Kei went to the pool with the rest of the class, getting especially close to Yōsuke, which possibly indicates that they have been dating since. She tried asking Kikyō to lend her points along with some other girls of the class to buy herself the 'essentials', in which at least Kikyō complied with the demand. She is seen getting closer to Yōsuke then proceeding to take the mid-test exams and passing with an overall score of 75.
During the anime pool filler episode, Kei saw Suzune walking out of the apartment building, claiming how there were rumors she had died, since no one had seen her over summer break. Kei then left, dragging Yōsuke with her after Suzune expressed her disinterest in hanging out with the rest of her class when being questioned about it.
Later Kei, like all the other first years, took part in the school cruise, where she was seen calling Yōsuke over to hang out with her friends. When the cruise ship headed to an island, all first-year students were told they need to survive for more than a week with basic materials. Kei got into an argument with Teruhiko Yukimura about the hygienic materials they would need for survival, specifically the need of a toilet. Kanji Ike joined the argument as well but after setting up camp, he surprised Kei, as he apologized for his words since he went through a similar event when camping as a child. Touched by this, Kei apologized for not understanding his reasons as well.
Towards the end of the survival test week, Kei was found crying in the girl's tent as her underwear was apparently stolen. The girls of her class had Yōsuke check all the boys and their luggage to find it. After minutes of searching, Yōsuke then found the underwear in Kiyotaka Ayanokōji's luggage but refrained from telling anyone, since he (rightfully) suspected that Ayanokōji was set up by someone else.
The next day, Kei and the other girls told the boys to build a separate camp from them because of the incident the day before. Kei had Yōsuke watch over the boys in the class while they moved, but Suzune requested that another boy should check over Yōsuke, since he could potentially be a threat as well. Though Kei defended her boyfriend, she agreed to the request, but wondered which boy should help as all the other boys are deemed untrustworthy. Suzune then proposed that Kiyotaka be the second guard since he doesn't seem to have a lecherous side.
Kei recalled that Kiyotaka was often 'invisible' during class, admitting to herself that she barely noticed him being their classmate. In the same night, somebody had started a fire at camp by burning the survival test manual, Kei and the other girls questioned the culprit's identity, first suspecting that one of the boys must have done it. They soon however, suspected Mio Ibuki because of she was nowhere to be found during the incident. They later learned that Suzune had dropped out of the test because of a fever. They then discussed Mio's motive and whether or not she was the actual culprit and C-Class' leader since her class had dropped out of the test earlier in the week.
The next morning, Kei was seen cleaning in the camp along with the girls. At the time of the class points announcement, she and the entire class were shocked to hear that D-Class came in first place. Later that same day on the cruise ship, Kei and the others thanked Suzune for her brilliant plan, unbeknown to them that Kiyotaka actually planned everything but gave Suzune all the credit to boost her popularity in the class cementing her place as a dependable leader.
In the light novel, there was another exam on the ship after their return from the survival island. In this exam, their objective was to find a traitor hidden among the groups that were divided into 12 difference groups based on Chinese zodiac's name among all classes. Kei was put into the same group as Kiyotaka, Teruhiko Yukimura, Hideo Sotomura, and students from other classes such as Honami Ichinose from B-Class, Machida from A-Class, and Mio Ibuki and Shiho Manabe from C-Class. Kei couldn't hide her dissatisfaction when seeing Kiyotaka and others as her groupmate.
Kei was seen to not taking any part of the group discussion to expose the traitor, but she was often seen flirting with the handsome Machida from the A class, which eventually pissed off Manabe and her C class friends. Machida seems to taken interest in Kei due to her cuteness and he had shown a protective behavior toward Kei. Manabe and her friends then brought up the topic of how Kei shoved one of her friend, Rika, and asks for her apology. Kei then feigned ignorance and kept using Machida as a shield, which further pissed Manabe up.
After one of their group meeting, Kiyotaka and Teruhiko saw Kei getting dragged into the emergency stairs and getting confronted by Manabe and others. Manabe was still confronting Kei about the incidence that happened to Rika, but Kei was being stubborn and neglected the fact that she pushed Rika. As the argument got heated up, Manabe and others lost their patient and started making physical contact to Kei. It was something like a little shove in the shoulder, but it caused Kei to show strange symptoms. Her breath was getting ragged and she squatted down and held her head and was cowering low. Manabe and her friends then proceeded to grab her hair and forcefully pulled Kei up, and they were saying things like wanting to messed her face up. This act of physical bullying really caused Kei to lose her previous arrogant acts and attitude. Kei was now shaking and tearing up to the point where the previous Karuizawa Kei seemed nothing more than a façade. Before the situation turned to the worse, Teruhiko, who couldn’t bear to watch it anymore, came to interrupt them. The situation did not get better until Kiyotaka said he saw a teacher and said it was better for them to leave. Manabe and others left, and Kei recovered. She then brushed off Teruhiko, who showed concerns, and told him and Kiyotaka to not let anyone know about this.
Kiyotaka thought that Kei's reaction is too extreme, he asked Hirata and learned about her past that she had been bullied since elementary school. As he learn that Kei is capable person that be able to continued covering her past using new persona up until now, he decided to make her his pawn which will completely obey his order secretly. He anonymously testified to Manabe about their issue, then used Hirata's phone to lure Kei to ship basement near engine room and let Manabe group revenge for their friend. After Manabe group left, he approached Kei and told her that he will save her, in exchange, she will obey all orders. Kei tried to put up strong front, but Kiyotaka glare deeply into her eye making her lose any will to resist. He secretly took video when Manabe bullying Kei at staircase, so he save Kei by blackmailing Manabe group not to approach or speak anything about Kei. Finally forming relationship with Kei, he firstly made her go along with his plan making A-class wrongly guessed the group traitor.
- (Monologue) "The arrow of love I had let loose. If it hits, it's a magical arrow that will cause one to fall in love. This one arrow, one way or another I'll make sure to hit Kiyotaka with it." 
- (Monologue) "Jeez ... inside my heart, there was another me who was squealing while running around. There's no more mistaking it. I just have to admit it now. Seriously, seriously, seriously, my heart's seriously been stolen away. The arrow which had pierced my heart. The arrow of love which I could no longer take out. Is this even possible? Is it even fine for me to fall in love with someone who's been partly bullying me? But it's already too late. The power of this arrow is tremendous. I have, I have towards Kiyotaka-----really, seriously, I've fallen in love with him. 
- The name Kei means "favor, benefit" (恵).
- As D-Class is for those with defective traits, Kei's defect is her low grades and for previous absences during middle school.
- Kei ranks #8 in the "Female Character" category in the 2019 edition of Takarajimasha's Kono Light Novel ga Sugoi! guidebook.
- In the 2020 edition, she is ranked #1.
- ↑ 1.0 1.1 You-Zitsu Anime — Episode 1
- ↑ You-Zitsu Anime — Episode 2
- ↑ You-Zitsu Anime — Episode 7
- ↑ You-Zitsu Anime — Episode 8
- ↑ You-Zitsu Anime — Episode 9
- ↑ You-Zitsu Anime — Episode 10
- ↑ You-Zitsu Anime — Episode 11
- ↑ You-Zitsu Anime — Episode 12
- ↑ You-Zitsu Light Novel — Volume 4
- ↑ You-Zitsu Light Novel — "The Cupid Karuizawa" Short Story
- ↑ You-Zitsu Light Novel — "Realised Feelings" Short Story
|Homeroom Teacher||Sae Chabashira|
|Class Representatives||Suzune Horikita • Yōsuke Hirata|
|Students||Kiyotaka Ayanokōji • Kikyō Kushida • Airi Sakura • Kei Karuizawa • Rokusuke Kōenji • Ken Sudō • Kanji Ike • Haruki Yamauchi • Teruhiko Yukimura • Akito Miyake • Haruka Hasebe • Mei-Yu Wang • Kokoro Inogashira • Maya Satō • Hideo Sotomura • Chiaki Matsushita • Satsuki Shinohara • Kayano Onodera • Nene Mori • Wataru Ijūin • Ryōtarō Hondō • Soshi Miyamoto • Kyōsuke Okiya|