In the year 20XX AD, Tokyo is nothing but a dystopic wasteland overrun by living corpses known as the Undead. Here we find two sisters who descend from a long line of expert swordsmen, yet were born to different mothers. The elder sister, Aya, was raised by her father, who subjected her to rigorous training in the way of the blade. Meanwhile, the younger sister, Saki, was raised by her mother, learning to despise her father for abandoning them and taking her sister away.
When her father goes missing, Aya decides to put her skills with the sword to use as an Undead-hunter. Upon her beloved mother's murder, Saki becomes consumed to the point of insanity with a desperate thirst for revenge, resorting to manipulating the Undead to achieve her goal.
Aya resolves to seek out her younger sister, her only surviving relation, while Saki is determined to resurrect her mother using an ancient art passed down through the ages. This art, however, requires the heart of a blood relative to work, meaning that the younger sister must kill the elder if she is to have her sworn vengeance.
And so, amidst a swirling storm of love, hate, and intrigue, the battle between the two sisters begins.