Kei Karuizawa

Kei Karuizawa is a student of Class 1-D. She sits in the second row, the second seat from the left, next to Yōsuke Hirata (Kei's "boyfriend").

Background
Despite her prominent figure in class and her constantly outgoing personality on the surface, Kei has a dark and unforgiving past as she was bullied throughout middle school, which leaves her with emotional scars that grew into a trauma and it haunted her until high school.

Appearance
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 has a scar on the right side of her torso, stemming from the bullying she endured from middle school.

Personality
Kei is an outgoing person who spends most of her time with the girls at school and Yōsuke Hirata (Kei's fake 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.

Abilities
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.

Plot
In her anime debut, 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. Suzune then monologue how Kei acted in class, pointing out that she led one of the two girl groups along with Kikyō and how dating Yōsuke greatly increased her influence in the class, casually implying that she was likely to be dating him for this reason only. 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.

Quotes

 * (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.

Trivia

 * 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 's  guidebook.