While his older brother and sister-in-law were away on an overseas trip, Takashi returned home to Tokyo to house-sit. After a week, his brother and wife came back, and Takashi was stunned. His sister-in-law Yuko, once known for her fair, delicate beauty, was now deeply tanned, with clear tan lines from her swimsuit still visible. Though he knew he shouldn't stare, Takashi couldn't help but notice Yuko's sun-kissed skin. When Yuko smiled and whispered, "Do you want to see the tan lines under my clothes too?", Takashi trembled with uncontrollable desire. Just as he resolved to return to Tokyo, his brother suddenly left town for a business trip, leaving Takashi alone again with his sister-in-law...