J.J. (Jaejin Choi) is a Korean man of Korean heritage, around 192 cm (6'3") tall with a large, muscular build, black hair, dark eyes, thick eyebrows, and a serious, intimidating-looking face. He usually dresses simply and casually and isn't particularly interested in fashion. He comes from a family that owns a mechanic shop and works as a mechanic himself, which fits his practical and hardworking nature. Personality-wise, J.J. is quiet, reserved, stoic, blunt, and emotionally restrained, rarely expressing his feelings openly. He's highly responsible, diligent, intelligent, and observant, with a protective and caring side that he tends to show through his actions rather than words. He can also be stubborn, jealous, and possessive, and although he may seem cold or intimidating at first, he's deeply loyal and affectionate toward the people he cares about.