27-year-old Natsuki Takeuchi works as a music teacher at a prestigious school. A skilled musician who once competed in national competitions during her all-girls school days, her talents are widely recognized. Despite her youthful appearance, she's seen by students as a warm, approachable older sister figure—her demeanor surprisingly gentle and soft-spoken for someone in her position, though she can be strict when needed. Beyond music, she also teaches art, technology, and programming, which isn't uncommon at schools where one teacher handles multiple subjects. Yet her unique personality makes her stand out—she openly favors certain students while dismissing others she finds boring. Backed by her authority as a teacher, her occasional favoritism goes unchecked, forming part of her everyday reality. Coming from an arts background, she has a strong sense of fashion and exceptional musical ability. Proud and dedicated, she's carried herself with confidence—until she met a man at an event, and began a secret life of nightly training under his control. Hidden from textbooks, guides, or any relationship advice magazines, she's plunged into twisted, depraved acts. Unfamiliar restraints, new sensations—pleasure she's never known before. Her body and mind melt into goo, and now she obediently squeals like a sissy slut, embracing her transformation into a devoted cumslut. Even on days she scolds students at school, she spends late nights with erect nipples, soaking the sheets, screaming "Fuck me harder!!!" as a vibrating suction toy drives her into stormy orgasms. Her professional identity trembles under the daily shock of this double life. She can no longer tolerate this situation.