妹のりむは恥ずかしがり屋で、家族の前でもおとなしいが、実は性に対する好奇心が旺盛で、兄のハジメに想いを寄せていた。ある日、ハジメは両親に、親戚の法事に行く間の留守番を任される。りむに想いを伝えられたハジメは、「俺ら兄弟だろ」と一度は跳ねのけるが、
Her younger sister, Norimu, is shy and quiet even in front of her family, but she is actually very curious about sex and has feelings for her older brother, Hajime. One day, Hajime’s parents assign him to watch over them while they go to a relative’s memorial service. When Hajime tells Rimu about his feelings for her, he brushes her off, saying, “We’re brothers, right?”