Mako returned to her parents' home to help with the housework while her mother was hospitalized. While chatting with her father, her younger brother returned home, but his attitude was strangely distant. Curious, Mako peeked into his room and discovered he had bought an onahole. Realizing he was a virgin because he didn't seem to know how to use it, Mako started teasing him, but she was suddenly pinned down by the raw power of a horny adolescent... From that day on, she was fucked relentlessly, at the mercy of her brother's insatiable sexual appetite...