Yuto had been a half-orphan when he eventually got a new stepmother and a new stepsister. He loved his new stepmother in particular. His stepsister was meant to take care of her stepbrother. But when his stepfather also vanishes, the two half are left to fend for themselves. Yet this turns out to be dangerous because at their age hormones are raging and soon a sexual relationship develops between the two of them. For Yuto it is great that his stepsister inherited her stepmother's big tits – as you can imagine she puts them to full use.