Shunsuke Aoba is a second-year middle school student transferring to Sunshine Academy. He arrives on a rest day, mistakenly believing the school empty, and encounters the significantly taller female student, Natsumi Asaoka. This meeting highlights their stark height difference: Shunsuke stands at 1.45 meters (4 feet 9 inches) while Natsumi reaches 1.80 meters (5 feet 11 inches).

Gruff, proud, and stubborn, Shunsuke demonstrates fierce determination and bravery, readily engaging in fights when provoked. Beneath his tough exterior, he possesses a fundamentally good heart. He harbors a fear of dogs and exhibits notable enthusiasm for eating.

Shunsuke initially expresses a general dislike for women, partly rooted in embarrassment over his family background; his mother operates a women's apparel shop where he reluctantly helps yet struggles to interact with female customers. Natsumi assists at the shop, earning his mother's approval. He frequently denies any romantic involvement with Natsumi despite her open affection, embodying a "She's Not My Girlfriend" dynamic.

His academic performance is poor, particularly in math, leading to conflict with a harsh teacher who mistreats lower-performing students. He occasionally lands in embarrassing situations, often functioning as a Butt-Monkey due to amusing injuries or accidents. Despite his short stature and initial dismissive attitude towards Natsumi's height, he experiences moments of accidental attraction towards her, distracted against his will by her physical appearance.

Over time, an underlying care for Natsumi develops beneath his gruff exterior, indicating a gradual emotional shift. He maintains a close friendship with classmate Kotaro Hayakawa, who admires Shunsuke's perceived masculinity and bravery. While projecting a tough image, Shunsuke's interactions reveal a capacity for loyalty and protective instincts, especially concerning those he values.