The Mukai siblings lost their parents when they were young. - Her older sister Ai continued to work hard, graduated from junior college, and became an office lady. - On the other hand, her younger brother Taichi was playful and didn't study well, but Ai was very fond of Taichi, who was her only family. - One day, Ai receives a call from a man named Nakata on her cell phone. - ``Your younger brother harmed the sister in our group.'' - Ai, who was called to make amends, is molested by Nakata and the others right in front of her younger brother, and is even forced to have sex with him...