S1 No.1 Style presents a steamy office romance featuring Nitori Hina, a stunningly beautiful and big-breasted office lady whose sharp demeanor during work hours hides a surprisingly sweet and affectionate side after hours. As a strict supervisor, she scolds her junior coworkers with a no-nonsense attitude, barking "Hey, why are you so slow with your work?!" But the moment the clock strikes quitting time, she softens instantly, saying warmly, "Good job today! Sorry I was so harsh earlier..." This striking contrast between her cold, professional exterior and her tender, loving after-work self creates an irresistible allure for her new male colleague. One evening, they end up staying late together—just the two of them. As the office grows quiet, her demeanor shifts dramatically. The stern senior melts into a doting, flirtatious woman, showering him with sugary affection. The tension between her "tsun" (aloofness) and "dere" (lovingness) builds an erotic charge that pushes him to the edge. When she gently whispers, "You've worked so hard today..." and then teasingly asks, "Want a reward... like sex?", how could he possibly say no? This is a full-throttle, seductive tsundere fantasy where the strictness of the workplace collides with the sweetness of private moments, driving her junior wild with desire. An intensely erotic drama that captures the ultimate office fantasy.