Shi Fen is a mischievous and academically capable first-year high school student, though his lazy tendencies often show. He delights in playful antics and pranks, frequently provoking his younger sister Shi Miao into physical confrontations where his foolish behavior earns him regular beatings. His personality blends sarcasm, wit, and immaturity, marked by a notable lack of common sense in daily situations, especially concerning food, which he prioritizes above nearly everything.

He exhibits cowardice when confronted, particularly by Shi Miao's violent reactions. Yet, he occasionally shows good intentions, like attempting to carry her after an injury, though these efforts typically backfire. Shi Fen lacks athletic ability, contrasting sharply with his sister's physical prowess, and is described as lazy, preferring leisure over exertion. Despite possessing a pleasant appearance, he struggles with popularity and has never had a girlfriend in high school.

His closest relationships include a deep friendship with Kai Xin, characterized by shared childishness and collaborative troublemaking like skipping restaurant bills or engaging in ridiculous schemes. He also befriends Wan Sui, a wealthy transfer student seeking normalcy, integrating him into their social circle for various escapades. Throughout the series, Shi Fen's bond with Shi Miao evolves from constant conflict to mutual reliance, revealing his underlying protective instincts. During significant challenges, he shows a caring side, prioritizing his sister's well-being despite their rivalry.

Character development occurs as Shi Fen matures, gradually displaying increased empathy and emotional awareness. He transitions from solely provoking Shi Miao to acknowledging her efforts and sacrifices, fostering a stronger sibling connection built on unspoken understanding and loyalty. His interactions shift from purely antagonistic to moments of genuine support, especially in crises, highlighting his role as a brother who, despite his flaws, consistently acts in his sister's best interests when it matters most.