The plot centres around a teenaged boy called Ayumu Narumi. Two years before the series, Ayumu's brother disappears without saying bye or where he would be although he did give one hint, the Blade Children.
Ever since then Ayumu had been trying to figure out what the Blade Children were or how they are connected to his brother. Ayumu meets a girl called Hiyono Yuizaki, who by the way is very nosy, and tries to help him find the Blade Children acting as a research assistant.
As we progress through the story, he meets all the Blade Children, all of which challenge him to different games that lead to life or death situations, and he finds out that they are all missing a seventh rib bone and have a curse of some sort. This just puts more questions in Ayumu's head. Will he ever find out the curse of the Blade Children? How is this connected to his brother? Only fate will tell.
We learn the Blade Children all 80 - the result of an IVF program by Yaiba Mizushiro who was a Blade Child himself -are born missing their 7th rib, possess cat like eyes and apparently have a mark on the right side of their body. All would grow up as geniuses in their own right, but one day their blood would awaken murderously and take over their self-will, becoming avatars of Yaiba.His organization split into three parties over the Blade Children Project:
- The Savers supported Yaiba's goals and desire to create more Blade Children. With Yaiba's death, they sought to protect the fact the future had not been determined yet.
- The Watchers were neutral, wanting to observe the first batch of Children and gather results first.
- The Hunters were against Yaiba, and tried multiple times to assassinate him, but repeatedly failed. After Yaiba's death, they worked to eliminate the Blade Children because of their potentially dangerous natures.