Kei Karuizawa

Kei Karuizawa is among the students with excellent grades in class 1-D.

In the class, she sits in the second row, second seat from the left, next to her "boyfriend", Yōsuke Hirata.

Background
Despite her prominent figure in class and her constantly outgoing personality on the surface, she has a dark and unforgiving past. She was the central victim of multiple bullying incidents back in her middle school days. This has left her with a scar and an emotional trauma that continues to haunt her. To prevent being bullied in her new high school life, she asked Yōsuke to be her fake boyfriend, to try and prevent any bullying from her new class.

Eventually, through a series of events, her target of support and protection switches to Kiyotaka.

Appearance
Kei is a teenage girl of average height with purple eyes and long blonde hair. While so, her hair is tied in a ponytail while the rest of it extends to her back. In her school uniform, she wears 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 also wears a blue ribbon around her collar. In a more casual clothing set, she simply wraps her school blazer around her waist and rolls up her dress shirt sleeves.

It's revealed that Kei has a scar on her left torso from the bullying she endured in middle school.

Personality
Kei is an outgoing person, spending most of her time with the girls at school and Yōsuke, her "boyfriend". She is also someone who speaks for the girls in the class, acting as one of the leaders along with him 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 actions, asked the girls of her class to lend her some money to buy the 'essentials', managing to get at least 2000 points from Kikyō Kushida.

She apparently doesn't take notice of less prominent people in the class, this was seen where she took note of Kiyotaka Ayanokōji being "invisible" after Suzune nominated him as a guard with Yōsuke. Ironically, she befriended him in the light novels and they are very close even going on a first name basis.

Abilities
She was assessed as being subpar by the school. Her absences and grades were the direct reason for her being placed in D-Class. She doesn't like academics or 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 Karuizawa, 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 asked the class to introduce themselves, agreeing with the idea.

After Sae Chabashira had 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 surprised why they didn't receive the monthly allotment of points, looking depressed throughout the explanation of S-Points and how D-Class failed to keep any of their points.

Some point later, Kei went to the pool with the rest of the class, getting especially close to Yosuke Hirata, possibly indicating that they were dating since just before this time. 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 proceeded to take the mid-test exams and passed with an overall score of 75.

During the anime pool filler episode, Kei saw Suzune walk out of the apartment building, claiming how there were rumors she had died because no one had seen her over summer break. Suzune then monologue how Kei acted in class, leading 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 dating him for this reason only (which also implied that they have been dating since before summer break if the latter statement's influence has been noted. Also, unknown to Suzune, but there was more to the relationship than expected). Kei then left, dragging Yōsuke with her after Suzune expressed her disinterested comments about hanging out with the rest of her class when questioned about it.

Kei, like all the other first years from every class, later 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, the 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 toilet situation. That soon extended to Kanji Ike as well but after setting up camp, Kanji apologized for his words since he went through similar as a child, as she apologized for not understanding his reasons.

Towards the end of the survival test week, Kei was found crying in the girl's tent as her underwear was apparently stolen and the girls of her class have Yōsuke check the suspected boys for it but they aren't recovered, with only Yōsuke and Kiyotaka Ayanokōji knowing where they really were. The next day Kei and the other girls commanded the boys to separate from them due to the incident the day before. Kei had Yōsuke watch over the boys in the class while they moved, but Suzune requested another boy to watch Yōsuke since he could still potentially be a threat. Though Kei defended her "boyfriend", she agreed to the request, but wondered which boy should help as the rest seemed lecherous. Suzune then chose Kiyotaka since he doesn't have a lecherous side. While Kiyotaka was picked, Kei had noticed that Kiyotaka often went by being 'invisible' during class, admitting herself that she never acknowledged him in the time they've been classmates. That night, while somebody had started a fire at camp by burning the survival test manual, Kei and the other girls questioned the culprit's identity, suspecting that one of the boys had done it; however they soon started suspecting Mio Ibuki because of her absence. Later, they learned that Suzune had dropped out of the test due to her fever and discussed Mio's motive and whether she was the actual culprit and Class C's Leader since the class had dropped out of the test earlier in the week.

The next morning, Kei was seen cleaning up the camp along with other girls. At the time of the class points announcement, she and the entire class were both shocked and surprised because of Class D's first place result. Later that same day on the cruise ship, Kei and the others thanked Suzune for her brilliant plan that Kiyotaka had actually put into place but gave her all the credit to boost her popularity and allies among the class, unbeknownst to the rest of the class.

Trivia

 * According to the school, her being placed in Class D is due to her low grades and absences during middle school.