Mary returns home from Tokyo after a long time, and her brother Takashi welcomes her back. He is excited to see his sister's sexy body. His sister is a little innocent and naive, and doesn't know how to trust people. Apparently, she never had a boyfriend in Tokyo, so Takashi takes advantage of her personality and lies to her, saying, "If I don't have sex for a while, I'll call myself a second virgin and go back to being a virgin."
