"Be my ideal girl.” It's been two months since childhood friends Yuuka and Kouta started dating. However, due to their inexperience, their "first time" together doesn’t go as planned. Enter Kouta’s younger sister, determined to ensure the couple’s happiness. No matter the cost. A boy, a girl, and his younger sister. All caught in a love triangle so sensual and immoral, you’ll want to look away. Yet you won’t be able to.