Since they were kids, Saya has always looked up to her kind, gentle older brother, Shou. He always looked after her, put her needs first, they spent all of their time together, and ultimately he was the only one who was ever there for her. Even without parents, 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.

Shou, on the other hand, can't stand to see his sister in such a state, locked away in their own home and forced into solitude. And so he 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. He becomes an expert at hunting vampires, driven by his sole desire to make his sister human again.

But Shou has another reason for wanting to get out of the house. Since she was bitten, Saya has become increasingly obsessed and forceful. She can't stand being mere siblings anymore, and with her actions becoming more forward and deliberate, her brother himself 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?