Toshiyuki Karasawa attends Sanada North High School, serving on the student council. He lives next door to Habara, with Takahiro residing a few houses away. His childhood at East Yada Elementary was marked by severe bullying, primarily from female classmates, leaving multiple bodily scars across his chest, arms, and lower back. The most traumatic event involved an attack by a figure called the Archdemon, who struck his forehead with a stick. This caused profuse bleeding and left a large, permanent scar between his eyes. To conceal this forehead scar, Karasawa constantly wears a distinctive grey, wide-brimmed cap. He maintains this habit at all times, including while sleeping or in hot springs, meaning many friends have never seen him without it. His appearance features a lean, tall build, spiked brown hair (depicted as black in some manga art), brown eyes, and an often un-tucked school uniform. His stern resting expression, partially hidden by the cap, contributes to an intimidating demeanor. Earlier depictions, like beach scenes in manga and anime, lack the later-mentioned body scars. At school, Karasawa displays a stiff, serious personality, strictly adhering to rules and diligently performing his duties. Outside school, he relaxes considerably, engaging in activities like role-playing with his friend Motoharu. These sessions sometimes lead to misadventures, such as attempting risky moves inspired by the anime *Kinnikuman*. He is polite, courteous, and excessively helpful—a trait prompting Motoharu to chastise him. His quick thinking proves valuable in crises, like maintaining order during a school festival fight or staying calm during a nighttime woodland exploration. His childhood trauma deeply influences his behavior; encounters with past bullies trigger strong physical reactions, including profuse sweating or nausea. He sometimes leverages these experiences sternly, using his scars to blackmail former tormentors. Despite this trauma, he displays an aptitude for interacting with girls, often distracting them with expired chocolates. He is implied to have secured a date during a beach trip. Karasawa ranks as the fifth-most featured character in the manga, appearing in 30 of 139 chapters. He achieved first place in a popularity poll with 48,806 votes, a significant lead. His cap independently received five votes in the same poll. He is typically referred to as "Karasawa" in the main series but "Toshiyuki" in the spin-off *High School Girls are Funky*. Although he appears in class photos, he is never depicted attending class in any media. The etymology of his surname combines "Kara" (唐, meaning China's Tang dynasty) and "Sawa" (沢, meaning marsh).