Kang Minjae (Protagonist) — Middle schooler. His family isn't poor, but he receives no separate allowance and can't bring himself to ask for things, so he always wears what he's given and uses what he's handed. Nearly scores a perfect mark in English and science, and after tutoring in the summer of his first year, he masters even his weaker subject—math—climbing to rank 1 in his class and top 10 in the entire school by the third year. With great agility and core strength, he gradually stands out in basketball, relay races, and pull-ups, becoming a visible presence across the whole school without even realizing it. Clumsy at expressing his emotions, he stubbornly underestimates his own charm, and even when he likes someone, he has no idea how to translate that feeling into action. His core deficiency is 'an inability to believe that attention is directed at him.' [Relationship with Yoon Haeun] His first love. He's been fixated on her since the day she sat behind him, but concludes that someone as famous in the city as Haeun could never like him. He writes off all of Haeun's questions, gifts, cards, worry, and jealousy as 'just being friendly' or 'just finding it fascinating,' ultimately failing to give it a name. [Relationship with Lee Junseok] Haeun's seatmate and a friend who liked her. Valuing his friendship, he deliberately keeps his distance from Haeun, but after a fight on the soccer field, they cry and reconcile, becoming even closer friends. [Relationship with Park Junho] Best friends who stood side-by-side by height number on the very first day of school. Because he trusted him the most, he shatters the hardest when he belatedly discovers he secretly dated Haeun. [Relationship with Jung Siwoo] An overwhelming friend and his subconscious benchmark. The thought that 'if a girl likes someone, it must be a guy like Siwoo' makes him even less able to trust Haeun's signals. [Relationship with Choi Seoyeon] A friend who told him the truth and the person who later teaches him how to properly name a relationship. [Relationship with Oh Eunju] The homeroom teacher who believed in and cherished him. He respects her deeply from the bottom of his heart.
Yoon Haeun — Minjae's first love. Assistant vice-president of her class in the first year, she isn't just the prettiest girl in class—she's famous across the entire city, a striking female student that students from other schools even come to look at. While she's used to being the center of attention and highly popular, she can't bring herself to speak her own heart aloud. Following the IT technician certificate incident, she begins constantly throwing questions at Minjae, shows off the small pen Minjae gave her in the girls' restroom, always prepares return gifts, and hands him a card on the last day of school before winter break reading 'My eternal partner,' telling him, 'Read this when you get home.' She notices when Minjae is sick or hurt before anyone else, tells him 'Don't hang out with other girls,' asks him to deliver a support speech for the student council president election, and calls him aside on sports day to cheer him on. The crucial point is that she is never a villain. She is simply a figure who sent signals, but grew tired and wavered when Minjae ultimately failed to make a move. [Relationship with Minjae] Maintains a strong favorable attitude from the first year to the middle of the second year, but grows weary as their relationship drifts aimlessly without a name. [Relationship with Park Junho] In the winter of their second year, as Junho—who is emotionally adept—moves in proactively, they secretly begin dating, which leads to a public relationship in their third year. [Relationship with Lee Junseok] First-year seatmate. Vaguely senses Junseok's affection, but her gaze remains fixed on Minjae in the front row. [Relationship with Choi Seoyeon] Best friend. Observes the subtle relationship with Minjae from the closest range. Just a middle schooler, not yet mature enough to name her own emotions.
Choi Seoyeon — Haeun's best friend and the person who watched Minjae and Haeun's subtle relationship from the closest perspective. Calm and thoughtful, she refuses to get swept up in idle gossip and knows how to speak the truth. In their third year, she cautiously lets Minjae know the fact that Haeun and Junho secretly dated during the winter break of their second year—an act born not out of tattling, but from a desire to keep Minjae from being pointlessly tossed about any longer. A year later, she begins dating Minjae, becoming the person who teaches Minjae how to deal with relationships clearly for the first time. Far from being a mere 'replacement lover,' she is an entity that teaches honesty instead of evasion and silence. [Relationship with Minjae] A friend who delivered the truth and later a lover. [Relationship with Haeun] As her closest friend, she struggles between not wanting to hate Haeun and yet feeling compelled to tell Minjae the truth.
Jung Siwoo — A classmate in their first and second years and the overwhelming benchmark that lowers Minjae's self-perception. Rumored to be the best fighter in the entire school, he carries an imposing air, yet his good personality makes the other boys follow him readily. Ranked 1st in his class and top 4 in the school, and nearly the best at soccer and basketball across the entire school, so when he plays sports during lunch break, girls flock to cheer him on and shower him with bundles of gifts. A good friend who first approached Minjae and befriended him early in admission, he has no particular interest in Haeun. Far from being a villain, he is a loyal friend, but because of his overwhelming presence, Minjae subconsciously assumes 'if a girl likes someone, it has to be a guy like Siwoo,' making him unable to believe even Haeun's signals. [Relationship with Minjae] A friend who reached out a hand first. [Relationship with Haeun] Uninterested.
Lee Junseok — Haeun's seatmate in early first year who liked her, watching closest as her attention turned toward Minjae in the front row. Because of this, he is jealous of Minjae, but Minjae treasures Junseok as a dear friend and tries hard not to like Haeun until the card incident. At the end of the first year, they clash while playing soccer, but after crying and apologizing to one another, they reconcile and become even closer friends. Afterward, Junseok's attitude changes from keeping Minjae and Haeun in check to accepting them to a certain degree. Junseok stands in direct contrast to the later Junho. He was jealous but clashed, fought but cried and reconciled, and ultimately remained a friend. [Relationship with Minjae] A true friend who went from jealousy to reconciliation. [Relationship with Haeun] Had a unrequited crush, but put his feelings aside and stepped back.
Park Junho — Best friend who naturally became close when they were assigned numbers right before Minjae on the very first day of school based on height. A bit handsome, but not a strikingly famous type, and doesn't particularly enjoy sports. Instead, likely influenced by his older sister, he understands girls' psychology well, making conversations natural and allowing him to get along comfortably with anyone. A character who entered through relationship sense rather than specs. Even though he knows Minjae likes Haeun, while Minjae remains ambiguously stalled, Junho approaches Haeun more comfortably and proactively, secretly dating her in the winter of their second year. When the truth comes to light in their third year, after Minjae tells him, 'Date openly. I'll give up,' Junho somehow starts avoiding Minjae and slowly drifts away from the male friend group as well. Not a pure villain, but the friend who most quietly crossed the line. [Relationship with Minjae] The most trusted best friend and the cause of the fracture. [Relationship with Haeun] From secret relationship to public relationship.
Kang Taesung — First-year class president who likes Haeun, the assistant vice president. Because of this, he picks fights with Minjae or interferes with him, who is close to Haeun. However, he is not an outright villain, just an ordinary kid with childish jealousy and a competitive streak. While Junho represents a quiet internal fracture in the later half, Taesung acts as a noisy external noise in the first half, serving as an obstacle that makes Haeun's signals even harder to decipher. [Relationship with Minjae] Keeping in check and picking fights. [Relationship with Haeun] Has a unrequited crush, but expresses it clumsily and childishly.
Oh Eunju — Minjae's homeroom teacher and a true adult. She adores and trusts Minjae deeply, and is warm enough to secretly help cover tuition for students in difficult financial situations. When organizing group activities or seating charts, she naturally places Minjae and Haeun together; that choice, which looks like fate, actually stems from the teacher's trust and favorable view of Minjae. Minjae respects and follows her deeply in his heart. It is also her who asks Minjae for a favor in the staff room on graduation day. [Relationship with Minjae] A student she trusts and cherishes. Her seating arrangements keep placing Minjae and Haeun close together.
