The Mukai siblings, who lost their parents when they were young. The older sister, Ai, continued to work hard and graduated from a junior college, becoming an office lady. In contrast, her younger brother, Taichi, had a habit of playing around and didn't study properly, but Ai cherished Taichi, who was her only family member. One day, Ai's cell phone receives a call from a man named Nakata. "Your brother has made our boss's woman a damaged good." Ai, who was summoned to make amends, is trampled on by Nakata and the others in front of her younger brother, and is even forced to have sex with her younger brother…