No matter what, she wanted to satisfy her boyfriend's older sister, so she asked me to be her sex practice partner. (Nagase Asami, DVAJ-0029)

Asami, a late-blooming woman with little knowledge of sex, is troubled by her boyfriend's apparent lack of satisfaction. Her younger brother, who initially came to comfort her and discuss the matter, decides to let her observe his sister's penis, which she's never properly examined. However, both become aroused, engaging in masturbation, oral sex, and ejaculation. From that day on, the brother becomes her practice table. Knowing that this sibling relationship is problematic, Asami claims it's all for her boyfriend's sake. Meanwhile, the brother, wanting to have sex with his sister, tries every method to make her feel pleasure, finally crossing the taboo line…