In a quiet apartment, the tension between 姉ちゃん and 行くん reaches a breaking point. 姉ちゃん, the devoted older sister, has always been there for 行くん, raising him alone since the passing of their parents five years ago. But now, 行くん is in trouble—after applying for a part-time job through an SNS, he was lured into a shady "闇バイト" (dark part-time job), and now he's being threatened with a fate as dire as being killed if he doesn't complete the job. With no money to pay the debt and no way out, 姉ちゃん steps in, determined to help her younger brother no matter the cost.
She confronts the mysterious man behind the job, a stern and imposing figure who takes it upon himself to make 行くん pay the price for his mistakes. But 姉ちゃん isn't about to let her brother suffer alone. She agrees to take on the challenge, stepping into the role of 行くん's "女" (woman) for ten days, in exchange for his freedom. What begins as a promise quickly turns into a passionate and intense experience, filled with seduction, submission, and a deep emotional connection.
As the days pass, 姉ちゃん and 行くん find themselves drawn deeper into the world of the mysterious man, each encounter more intense than the last. The man, with his rough but caring nature, becomes a force of both torment and comfort, testing 姉ちゃん's limits and pushing her to reveal the depths of her devotion.
Through every challenge, every moment of pain and pleasure, 姉ちゃん remains steadfast, proving that love and sacrifice are the strongest forces of all. In the end, as the ten days come to a close, the bond between 姉ちゃん and 行くん is stronger than ever, and the man, recognizing her strength and heart, lets them go—free, together, and forever changed.
