Kento, who is about to leave for college in a month with his girlfriend, worries that he can't tell anyone...
He has never been able to make his partner cum. What's more, he can't figure out if she was even good with him.
"...At this rate, I'm going to get horns, just like in a hentai manga!!!"
While Kento was pondering this way, she appeared in front of him... his younger sister Mao, who seemed to have a lot of sexual experience.
"Ugh, okay~ I'll help you~"
And so begins the lustful relationship between Kento and his little sister.