Miyu is a caring older sister who lives in the same house as her two younger brothers. Each brother has a girlfriend and they get along well, but they are both struggling with the typical adolescent problem of not knowing what to do about sex. Younger brother (1) has a girlfriend, but sex with her isn't going well. He can't insert it easily. Younger brother (2) has a girlfriend for the first time in his life. He doesn't know how to interact with girls, let alone sex. He's still a virgin. Unable to bear seeing the two brothers like that, their kind older sister gives them some naughty instruction. However, since they're brothers, they only practice with dry sex, but the older sister gets so excited she can't hold back and inserts it!! And the younger brothers are surprisingly good at it, which surprises the older sister!! What if I cum from them?!