Shou, the older brother, and Saya, the litlle sister, only have each other. The two of them lived happily, enjoying their peaceful lives together. That is, until Saya was bitten.

When bitten by a pure-blooded vampire, the one who was bitten may themself become a vampire, as was the case with Saya. She can't leave the house out of fear that she will feast, and her brother must lock her away to protect her from vampire hunters, such as himself. The only solace she has is being taken care of by her beloved older brother, whom she knows has eyes only for her, and vice-versa.

And so, Shou has made it his goal to kill the pure-blooded vampire who bit his sister, believing that in doing so he may restore his sister to what she once was, and becomes an expert for that. But since Saya was bitten, she has become increasingly obsessed and forceful. She can't stand being mere siblings anymore, and Shou is having a hard time holding back.

Will Shou give in? Or will he kill the pure-blooded vampire first? And even if he does, will that be enough to stop the romance forming between the two of them?