Serina Yoshida has been Anna Yamada's close friend since their fourth year of elementary school. Her reserved and mature demeanor masks a keenly observant nature, catching subtle details others overlook—like Ichikawa Kyoutarou's prior familiarity with Yamada’s apartment. She typically wears her light-brown hair in a ponytail and stands as the second tallest among her friends, just shorter than Yamada. Yoshida’s street-style fashion projects a faintly intimidating, delinquent aura.

Protective of Yamada, she confronted Kanaoya Rin after a basketball incident, relenting only once Yamada received a sincere apology. Yoshida frequently moderates group dynamics, expressing exasperation at Kobayashi Chihiro’s obliviousness and intervening when Sekine Moeko’s teasing crosses lines—like halting Sekine’s fake-dating prank targeting Ichikawa and Yamada. She avoids Adachi Shou due to his perverted behavior, rejecting physical contact during a personality test and later uncovering his online motives with disgust. Despite this, she shares his and Sekine’s interest in the *Crows* manga.

Yoshida maintains neutrality toward Ichikawa, rarely interacting but lacking animosity. She once fixed his uneven haircut using Adachi’s wax, ignoring his protests. Gradually recognizing the mutual affection between Yamada and Ichikawa, she subtly supports them, approving Yamada’s wallet-chain gift choice.

Her interests span the school dance club, delinquent-themed manga, and Showa-era yakuza films. She favors red, enjoys fried chicken and grilled meat, and adores hamsters. Her favorite film is *Boys Be Ambitious*, and her idol is Nakabayashi Akina. In sixth grade, she declined a confession from an acquaintance’s older brother. Sekine has teased her about potentially pursuing hairstyling.