Kazuyoshi Usui and his younger brother, Masafumi, grew up alongside their close childhood friend, Sawa. During his first year of high school, Kazuyoshi began to feel overshadowed by Masafumi’s superior intellect and skill in science and electronics. When Sawa began receiving death threats from a stalker, she sought help from the brothers. Kazuyoshi, frustrated that Masafumi’s advice carried more weight, refused to accompany her when she went to buy self-defense equipment. As a result, Masafumi went with Sawa in his place.

While they were out, Sawa’s friend Yukino visited Kazuyoshi and revealed that Sawa’s stalker, a boy named Shinji, had previously stabbed a classmate in middle school and was rumored to still carry a knife. Concerned, Kazuyoshi called Masafumi to warn him and Sawa. However, Yukino’s reaction to hearing Masafumi’s name led Kazuyoshi to realize she might be emotionally involved with the situation. When Yukino suddenly spotted Shinji nearby, Kazuyoshi chased him down, only to discover that Shinji was merely an anxious admirer, not a violent criminal. From him, Kazuyoshi learned that it had actually been Yukino, not Shinji, who had committed the middle school stabbing. Realizing that Yukino was likely targeting Sawa, he rushed to find his brother and friend.

Kazuyoshi arrived too late. He found Masafumi being taken away by ambulance, fatally stabbed near the heart (stabbed in the back in the anime adaptation). Yukino had attacked Masafumi under the mistaken belief that he was Sawa’s boyfriend. Stricken with guilt, Kazuyoshi blamed himself for his brother’s death, believing that his refusal to accompany Sawa had led to the tragedy. In his grief, he cut his hair to resemble Masafumi’s and began wearing his brother’s glasses, removing the lenses to preserve them as a memento.

Kazuyoshi adopted Masafumi’s old nickname, “Switch,” as his own and eventually withdrew from society. He stopped speaking entirely, choosing to communicate through a computer voice synthesizer, and became a hikikomori. His reclusive state continued until Yusuke “Bossun” Fujisaki, the future leader of the Sket Dan, reached out to him and helped him find purpose again, marking the start of his return to normal life.

In his youth, prior to Masafumi’s death, Kazuyoshi Usui had a slightly longer and messier hairstyle and did not wear glasses. His appearance was casual but understated, and his clothing at home tended to be more formal and less relaxed than his later attire.

In the present, Kazuyoshi known by his nickname Switch is described as a handsome young man whose calm behavior and mysterious presence make him well-liked among his peers. He communicates exclusively through a voice synthesizer on his laptop, a trait that adds to his enigmatic reputation. His current look is intentionally modeled after that of his late brother, Masafumi, featuring a similar hairstyle and a pair of plastic-framed glasses without lenses. He typically wears his school uniform with a green vest layered over it, a signature element of his everyday appearance.

In his earlier years, Kazuyoshi Usui was laid-back, protective, and deeply devoted to his younger brother, Masafumi, and their childhood friend, Sawa. He displayed the composure and dependability expected of an older brother, though he quietly struggled with feelings of inadequacy. Kazuyoshi began to envy Masafumi’s creativity and ability to impress others, particularly Sawa. Following Masafumi’s death, he attempted to return to school but found the emotional strain unbearable. His homeroom teacher eventually advised him to attend only when he felt ready, marking the beginning of his reclusive period.

After overcoming his period of isolation and graduating from high school, Kazuyoshi now known as Switch became calm, reserved, and emotionally restrained. He rarely expresses visible emotion and often delivers remarks with a dry, deadpan tone. His use of a voice synthesizer to communicate contributes to his detached image, and his humor frequently relies on sarcasm and understatement. Despite this, he occasionally manipulates the pitch of his synthetic voice for comedic effect, revealing a subtle playfulness beneath his stoic behavior.

Switch is also portrayed as an avid anime enthusiast, capable of offering lengthy and humorous analytical commentary on various series featured within Sket Dance. Beneath his composure, he retains a sense of empathy and loyalty toward his friends in the Sket Dan, using his intellect to support them from behind the scenes. By the conclusion of the series, he is shown to have fully recovered from his past trauma and regained emotional stability.

Electronics Expertise
Kazuyoshi Usui, known as Switch, is highly skilled with computers and electronic devices. Using his laptop, he performs complex tasks with efficiency and precision, making him the technological backbone of the Sket Dan.

Tone Modification
Through his custom speech synthesis software, Switch can freely alter the tone and pitch of his computerized voice. He often employs this ability for comedic purposes, impersonations, or to create specific emotional effects during conversations.

Information Database
Switch maintains an extensive digital archive containing personal data about students and faculty at Kaimei High School. His encyclopedic knowledge extends beyond school matters to include pop culture, particularly anime and manga. Though he frequently denies being an otaku, his familiarity with the medium often becomes a running joke within the series.

Inventive Talent
Switch demonstrates exceptional proficiency as an inventor, creating a variety of unconventional gadgets and technological devices to assist the Sket Dan. His passion for invention is partly rooted in the loss of his younger brother, Masafumi, but his aptitude in engineering and creative design was evident even beforehand.

Yūsuke “Bossun” Fujisaki
Switch shares a deep bond with Yūsuke “Bossun” Fujisaki, the leader of the Sket Dan. Much like Himeko, he feels indebted to Bossun for helping him overcome his grief and isolation. Despite his eccentricities, Switch is unwaveringly loyal to Bossun and provides the group’s technical and analytical support. Though Bossun is not as invested in otaku culture, the two often discuss tokusatsu series and exchange anime DVDs, showing a shared appreciation for entertainment and creativity.

Masafumi Usui
Masafumi was Switch’s younger brother and the original bearer of the nickname “Switch.” Kazuyoshi introduced Masafumi to computers, but his brother quickly surpassed him in skill, impressing their mutual friend Sawa. While Kazuyoshi admired Masafumi, he also felt overshadowed by him. After Masafumi’s death in a stabbing incident, Kazuyoshi was consumed by guilt. As a tribute to his brother, he adopted Masafumi’s appearance and nickname, stopped speaking aloud, and began communicating exclusively through his laptop. This transformation marked both his mourning and his effort to preserve his brother’s memory.

Sawa Yamauchi
Sawa was the childhood friend of both Kazuyoshi and Masafumi Usui. Kazuyoshi harbored romantic feelings for her, but Sawa appeared closer to Masafumi, which fueled Kazuyoshi’s insecurities. Before moving away, Kazuyoshi confessed his love to Sawa, and she replied that she felt the same. Her connection to both brothers and the tragedy that followed profoundly influenced Switch’s emotional development and his decision to stop speaking.

Momoka Kibitsu
Momoka, an idol singer, develops romantic feelings for Switch over the course of the series. When asked why he attends all her concerts, Switch replies via sketchbook that he does so to support her, though she suspects this is a modest deflection. On Valentine’s Day, Momoka gives him honmei choco (chocolate given to one’s romantic interest) and thanks him for his encouragement. Switch initially insists he can never fall in love again, haunted by memories of Sawa. However, after coming to terms with his past and graduating high school, Switch begins to move forward and accepts Momoka’s feelings. The two eventually start dating.

Reiko Yūki
Reiko Yūki serves as Switch’s rival in the series. A firm believer in the occult, Reiko frequently challenges Switch’s scientific worldview by visiting the Sket Dan room to debate paranormal topics. Despite her loud and eccentric behavior, Switch remains calm and analytical, often disproving her claims through logic and evidence. Nevertheless, he has shown kindness toward Reiko, assisting her on personal matters such as helping her appear more confident before a boy she liked and exposing a fraudulent fortune teller’s tricks.